- Zn(II)-, Al(III)-, and Cu(II)-Catalyzed Decarboxylation of 2-Oxalopropionic Acid
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Distributions of species formed by the coordination of 2-oxalopropionic acid by Zn(II), Al(III), and Cu(II) ions are presented, and kinetics of decarboxylation are discussed in terms of the species present in solution.Studies of initial rates of metal ion catalyzed decarboxylation of 2-oxalopropionic acid (H2L) show dependence on the degree of formation of the metal chelate (ML).Rate constants (kML) for the decarboxylation of ZnL, CuL, and AlL+ were found to be 18.2 x 10-3 s-1, 21.0 x 10-3 s-1, and 9.51 x 10-3 s-1, respectively.The equilibrium constants for ML(keto) ML(enol) were evaluated for the Zn(II) and Al(III) systems and rate constants (kKML) for the decarboxylation of the active keto forms of the Zn(II) and Al(III) chelates were found to be 31 x 10-3 s-1 and 79 x 10-3 s-1, respectively.The decarboxylation rate constant for the 2:1 Al(III) chelate, AlL2-, was determined to be 33.5 x 10-3 s-1.The keto-enol equilibrium constant -(enol)>/-(keto)> was evaluated, and the decarboxylation rate constant of AlL2-(keto) was calculated as 43 x 10-3 s-1.
- Kubala, Gregory,Martell, Arthur E.
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- Nuclear Magnetic Resonance Investigation of the Spontaneous Decarboxylation of 2-Oxalopropionic Acid. 2. Species in Solution
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The kinetics of the spontaneous decarboxylation of 2-oxalopropionic acid (OPA) to the enolate intermediate of α-ketobutyric acid (AKBA) with subsequent ketonization, and β-deuteration via enolization, have been studied by NMR in aqueous solution at 31 deg C.The rate constants for the decarboxylation of the fully protonated, monoprotonated, and fully deprotonated species of OPA were found to be 1.67 * 10-5 s-1, 13.5 * 10-5 s-1, and 7.75 * 10-5 s-1, respectively.The rate constant for the ketonization of the intermediate was found to be 3.25 * 10-4 s-1 while the rate constant for the enolization of OPA was found to be 2.70 * 10-4 s-1.The ketonization and enolization processes exhibited specific acid catalysis and the second-order rate constants were found to be 1.60 * 10-1 M-1 s-1 and 1.20 * 10-1 M-1 s-1, respectively.The first pKa of OPA, involving the carboxyl adjacent to the keto function, was found to be 1.75, while the second pKa for the remaining carboxyl group was determined to be 4.18.In D2O the pK's were calculated as 2.38 and 4.50, respectively.Under the reaction conditions employed the hydrate species exists in appreciable concentrations at low pH while the concentration of the enol species was not significant.
- Kubala, Gregory,Martell, A. E.
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- Engineering methionine γ-lyase from Citrobacter freundii for anticancer activity
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Methionine deprivation of cancer cells, which are deficient in methionine biosynthesis, has been envisioned as a therapeutic strategy to reduce cancer cell viability. Methionine γ-lyase (MGL), an enzyme that degrades methionine, has been exploited to selectively remove the amino acid from cancer cell environment. In order to increase MGL catalytic activity, we performed sequence and structure conservation analysis of MGLs from various microorganisms. Whereas most of the residues in the active site and at the dimer interface were found to be conserved, residues located in the C-terminal flexible loop, forming a wall of the active site entry channel, were found to be variable. Therefore, we carried out site-saturation mutagenesis at four independent positions of the C-terminal flexible loop, P357, V358, P360 and A366 of MGL from Citrobacter freundii, generating libraries that were screened for activity. Among the active variants, V358Y exhibits a 1.9-fold increase in the catalytic rate and a 3-fold increase in KM, resulting in a catalytic efficiency similar to wild type MGL. V358Y cytotoxic activity was assessed towards a panel of cancer and nonmalignant cell lines and found to exhibit IC50 lower than the wild type. The comparison of the 3D-structure of V358Y MGL with other MGL available structures indicates that the C-terminal loop is either in an open or closed conformation that does not depend on the amino acid at position 358. Nevertheless, mutations at this position allosterically affects catalysis.
- Raboni, Samanta,Revtovich, Svetlana,Demitri, Nicola,Giabbai, Barbara,Storici, Paola,Cocconcelli, Chiara,Faggiano, Serena,Rosini, Elena,Pollegioni, Loredano,Galati, Serena,Buschini, Annamaria,Morozova, Elena,Kulikova, Vitalia,Nikulin, Alexey,Gabellieri, Edi,Cioni, Patrizia,Demidkina, Tatyana,Mozzarelli, Andrea
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- Unusual stereoselectivity of methionine-γ-lyase from Citrobacterfreundii toward diastereomeric (S)-methionine S-oxide
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Using a diastereomeric mixture of (S)-methionine S-oxide as an example, kinetic preference of methionine-γ-lyase toward a stereogenic center at the γ-sulfur atom of the (2S, RS) diastereomer was discovered for the first time.
- Faleev, Nikolai G.,Tsvetikova, Marina A.,Ilyin, Mikhail M.,Yufryakov, Vyacheslav S.,Kolotyrkina, Natal'ya G.,Kulikova, Viktoria V.,Demidkina, Tatiana V.,Kochetkov, Konstantin A.
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p. 236 - 238
(2021/05/04)
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- Photoinduced homolytic decarboxylative acylation/cyclization of unactivated alkenes with α-keto acid under external oxidant and photocatalyst free conditions: access to quinazolinone derivatives
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A novel and green strategy for the synthesis of acylated quinazolinone derivativesviaphoto-induced decarboxylative cascade radical acylation/cyclization of quinazolinone bearing unactivated alkenes has been developed. The protocol provides a novel route to access acyl radicals from α-keto acids through a self-catalyzed energy transfer process. Most importantly, the reaction proceeded smoothly without any external photocatalyst, additive or oxidant, and could be easily scaled-up in flow conditions with sunlight irradiation.
- Sun, Bin,Shi, Rongcheng,Zhang, Kesheng,Tang, Xiaoli,Shi, Xiayue,Xu, Jiayun,Yang, Jin,Jin, Can
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supporting information
p. 6050 - 6053
(2021/06/21)
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- Rational engineering ofAcinetobacter tandoiiglutamate dehydrogenase for asymmetric synthesis ofl-homoalanine through biocatalytic cascades
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l-Homoalanine, a useful building block for the synthesis of several chiral drugs, is generally synthesized through biocascades using natural amino acids as cheap starting reactants. However, the addition of expensive external cofactors and the low efficiency of leucine dehydrogenases towards the intermediate 2-ketobutyric acid are two major challenges in industrial applications. Herein, a dual cofactor-dependent glutamate dehydrogenase fromAcinetobacter tandoii(AtGluDH) was identified to help make full use of the intracellular pool of cofactors when using whole-cell catalysis. Through reconstruction of the hydrophobic network between the enzyme and the terminal methyl group of the substrate 2-ketobutyric acid, the strict substrate specificity ofAtGluDH towards α-ketoglutarate was successfully changed, and the activity obtained by the most effective mutant (K76L/T180C) was 17.2 times higher than that of the wild-type protein. A three-enzyme co-expression system was successfully constructed in order to help release the mass transfer restriction. Using 1 Ml-threonine, which is close to the solubility limit, we obtained a 99.9% yield ofl-homoalanine in only 3.5 h without adding external coenzymes to the cascade, giving 99.9% ee and a 29.2 g L?1h?1space-time yield. Additionally, the activities of the engineeredAtGluDH towards some other hydrophobic amino acids were also improved to 1.1-11.2 fold. Therefore, the engineering design of some dual cofactor-dependent GluDHs could not only eliminate the low catalytic activity of unnatural substrates but also enhance the cofactor utilization efficiency of these enzymes in industrial applications.
- Diao, Shiqing,Jiang, Shuiqin,Liu, Yan,Sun, Yangyang,Wang, Hualei,Wang, Liuzhu,Wei, Dongzhi
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p. 4208 - 4215
(2021/06/30)
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- Biocatalytic Cascade Reaction for the Asymmetric Synthesis of L- and D-Homoalanine
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Unnatural amino acids attract growing attention for pharmaceutical applications as they are useful building blocks for the synthesis of a number of chiral drugs. Here, we describe a two-step enzymatic method for the asymmetric synthesis of homoalanine from L-methionine, a cheap and readily available natural amino acid. First, the enzyme L-methionine γ-lyase (METase), from Fusobacterium nucleatum, catalyzed the γ-elimination of L-methionine to 2-oxobutyrate. Second, an amino acid aminotransferase catalyzed the asymmetric conversion of 2-oxobutyrate to either L- or D-homoalanine. The L-branched chain amino acid aminotransferase from Escherichia coli (eBCAT), using L-glutamate as amino donor, produced L-homoalanine (32.5 % conv., 28 % y, 99 % ee) and the D-amino acid aminotransferase from Bacillus sp. (DATA) used D-alanine as amino donor to produce D-homoalanine (87.5 % conv., 69 % y, 90 % ee). Thus, this concept allows for the first time the synthesis of both enantiomers of this important unnatural amino acid.
- Silva, Marcus V. de M.,Costa, Ingrid C. R.,de Souza, Rodrigo O. M. A.,Bornscheuer, Uwe T.
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p. 407 - 411
(2018/11/01)
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- Electrochemical synthesis of enaminones: Via a decarboxylative coupling reaction
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An environmentally benign and efficient electrochemical synthesis of enaminones via a decarboxylative coupling reaction of α-keto acids using n-Bu4NI as a redox catalyst and electrolyte under constant current electrolysis in an undivided cell is reported. A broad vinyl azide substrate scope and high functional group tolerance are observed. A gram-scale reaction further demonstrates the practicability of the protocol. The results of cyclic voltammetry and control experiments indicate that I2 is likely the active species to initiate the oxidative decarboxylation via an acyl hypoiodite intermediate.
- Kong, Xianqiang,Liu, Yulong,Lin, Long,Chen, Qianjin,Xu, Bo
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supporting information
p. 3796 - 3801
(2019/07/31)
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- One-Pot Preparation of d-Amino Acids Through Biocatalytic Deracemization Using Alanine Dehydrogenase and Ω-Transaminase
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d-Amino acids are pharmaceutically important building blocks, leading to a great deal of research efforts to develop cost-effective synthetic methods. Preparation of d-amino acids by deracemization has been conceptually attractive owing to facile synthesis of racemic amino acids by Strecker synthesis. Here, we demonstrated biocatalytic deracemization of aliphatic amino acids into d-enantiomers by running cascade reactions; (1) stereoinversion of l-amino acid to a d-form by amino acid dehydrogenase and ω-transaminase and (2) regeneration of NAD+ by NADH oxidase. Under the cascade reaction conditions containing 100?mM isopropylamine and 1?mM NAD+, complete deracemization of 100?mM dl-alanine was achieved after 24?h with 95% reaction yield of d-alanine (> 99% eeD, 52% isolation yield). Graphical Abstract: [Figure not available: see fulltext.].
- Han, Sang-Woo,Shin, Jong-Shik
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p. 3678 - 3684
(2018/10/20)
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- Highly atom economic synthesis of D-2-aminobutyric acid through an in vitro tri-enzymatic catalytic system
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D-2-Aminobutyric acid is an unnatural amino acid serving as an important intermediate in pharmaceutical production. Developing a synthetic method that uses cheaper starting materials and produces less by-product is a pressing demand. A tri-enzymatic catalytic system, which is composed of L-threonine ammonia lyase (L-TAL), D-amino acid dehydrogenase (D-AADH), and formate dehydrogenase (FDH), has thus been developed for the synthesis of D-2-aminobutyric acid with high optical purity. In this cascade reaction, the readily available L-threonine serves as the starting material, carbon dioxide and water are the by-products. D-2-Aminobutyric acid was obtained with >90% yield and >99% enantioselective excess, even without adding external ammonia, demonstrating that the ammonia from the first reaction can serve as the amino donor for the reductive amination step. This multi-enzymatic system provides an attractive method with high atomic economy for the synthesis of D-α-amino acids from the corresponding L-α-amino acids, which are readily produced by fermentation.
- Chen, Xi,Cui, Yunfeng,Cheng, Xinkuan,Feng, Jinhui,Wu, Qiaqing,Zhu, Dunming
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p. 534 - 540
(2018/08/17)
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- Asymmetric C-Alkylation by the S-Adenosylmethionine-Dependent Methyltransferase SgvM
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S-Adenosylmethionine-dependent methyltransferases (MTs) play a decisive role in the biosynthesis of natural products and in epigenetic processes. MTs catalyze the methylation of heteroatoms and even of carbon atoms, which, in many cases, is a challenging reaction in conventional synthesis. However, C-MTs are often highly substrate-specific. Herein, we show that SgvM from Streptomyces griseoviridis features an extended substrate scope with respect to the nucleophile as well as the electrophile. Aside from its physiological substrate 4-methyl-2-oxovalerate, SgvM catalyzes the (di)methylation of pyruvate, 2-oxobutyrate, 2-oxovalerate, and phenylpyruvate at the β-carbon atom. Chiral-phase HPLC analysis revealed that the methylation of 2-oxovalerate occurs with R selectivity while the ethylation of 2-oxobutyrate with S-adenosylethionine results in the S enantiomer of 3-methyl-2-oxovalerate. Thus SgvM could be a valuable tool for asymmetric biocatalytic C-alkylation reactions.
- Sommer-Kamann, Christina,Fries, Alexander,Mordhorst, Silja,Andexer, Jennifer N.,Müller, Michael
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supporting information
p. 4033 - 4036
(2017/03/27)
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- Enzymatic Resolution by a d-Lactate Oxidase Catalyzed Reaction for (S)-2-Hydroxycarboxylic Acids
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Oxidase-catalyzed kinetic resolution is important for the production of enantiopure 2-hydroxycarboxylic acids (2-HAs), which are versatile building blocks for the synthesis of many significant compounds. However, in contrast to that of (R)-2-HAs, the production of (S)-2-HA is challenging because of the lack of related oxidases. Herein, suitable enzymes were screened systematically through the analysis of numerous putative d-lactate oxidase sequences and identification of several required properties. Finally, a d-lactate oxidase from Gluconobacter oxydans 621H with advantageous characteristics, such as good solubility, broad substrate spectrum, and high stereoselectivity, was selected to resolve 2-HAs into (S)-2-HAs. A variety of (S)-2-HAs was produced successfully using this d-lactate oxidase with excellent enantiomeric excess values (>99 %). The presented screening criteria and approach for target biocatalysis suggested a guideline for the production of optically active chemicals such as (S)-2-HAs.
- Sheng, Binbin,Xu, Jing,Ge, Yongsheng,Zhang, Shuo,Wang, Danqi,Gao, Chao,Ma, Cuiqing,Xu, Ping
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p. 2630 - 2633
(2016/08/30)
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- Preparation of d-threonine by biocatalytic kinetic resolution
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D-Threonine is one of the important unnatural amino acids used as chiral building blocks in pharmaceutical drugs. Owing to the presence of two chiral centers, a synthetic protocol, either through chemocatalysis or biocatalysis, has not yet been available for one-step preparation of stereochemically pure d-threonine in terms of enantiomeric and diastereomeric excesses (i.e., both >99%). Here we demonstrate that facile production of d-threonine can be implemented using threonine deaminase (TD) via kinetic resolution of dl-threonine that can be readily prepared by conventional organic synthesis. TD catalyzes the dehydration/deamination of l-threonine, leading to generation of 2-oxobutyrate and ammonia. In contrast to mild substrate inhibition of the TD activity by l-threonine (i.e., apparent inhibition constant (KIapp) = 950 mM), d-threonine turned out to be a strong inhibitor (i.e., KIapp = 41 mM). In addition to the enzyme inhibitions by both enantiomers of threonine, cell lysis observed during small-scale kinetic resolutions of ≥1 M dl-threonine led us to carry out a preparative-scale reaction at 500 mM racemic substrate. The preparative-scale kinetic resolution in a 50 mL reaction mixture charged with 3 g dl-threonine and 3400 U whole cells was completed at 5 h with >99% ee of d-threonine. Product isolation by a cation-exchange chromatography led to white solid of d-threonine (1.36 g, 90.7% isolation yield). To explore whether our strategy could afford coproduction of another valuable unnatural amino acid, the pass-through solution from the cation-exchange column was further processed by a ω-transaminase (ω-TA) reaction where 2-oxobutyrate was converted to enantiopure homoalanine using isopropylamine as an amino donor. Addition of S- and R-selective ω-TA to the pass-through solution led to 93.2 and 90.9% reaction yield within 12 h with both >99% ee of the produced l- and d-homoalanine, respectively.
- Han, Sang-Woo,Shin, Jong-Shik
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p. 227 - 232
(2015/10/28)
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- Preparation method of optically active amines and homoalanine
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The present invention refers to optically active relates to manufacturing method of a chiral amine. The present invention according to manufacturing method whereby an optical active chiral for producing an amine when the low-cost amino receptor by using production thereof in the preparation of optically active chiral amine USB data switches a, such low-cost amino receptor using primer even optically active excellent manufacturing efficiency of a chiral amine.. In addition single enantiomers of is connected with a, furthermore said manufacturing method is naturally through the file does not exist at L- [...] production and..
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Paragraph 0048
(2017/01/02)
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- The Ala95-to-Gly substitution in Aerococcus viridans l -lactate oxidase revisited - Structural consequences at the catalytic site and effect on reactivity with O2 and other electron acceptors
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Aerococcus viridansl-lactate oxidase (avLOX) is a biotechnologically important flavoenzyme that catalyzes the conversion of l-lactate and O2 into pyruvate and H2O2. The enzymatic reaction underlies different biosensor applications of avLOX for blood l-lactate determination. The ability of avLOX to replace O2 with other electron acceptors such as 2,6-dichlorophenol-indophenol (DCIP) allows the possiblity of analytical and practical applications. The A95G variant of avLOX was previously shown to exhibit lowered reactivity with O2 compared to wild-type enzyme and therefore was employed in a detailed investigation with respect to the specificity for different electron acceptor substrates. From stopped-flow experiments performed at 20 °C (pH 6.5), we determined that the A95G variant (fully reduced by l-lactate) was approximately three-fold more reactive towards DCIP (1.0 ± 0.1 × 106 M-1·s-1) than O2, whereas avLOX wild-type under the same conditions was 14-fold more reactive towards O2 (1.8 ± 0.1 × 106 m-1·s-1) than DCIP. Substituted 1,4-benzoquinones were up to five-fold better electron acceptors for reaction with l-lactate-reduced A95G variant than wild-type. A 1.65-? crystal structure of oxidized A95G variant bound with pyruvate was determined and revealed that the steric volume created by removal of the methyl side chain of Ala95 and a slight additional shift in the main chain at position Gly95 together enable the accomodation of a new active-site water molecule within hydrogen-bond distance to the N5 of the FMN cofactor. The increased steric volume available in the active site allows the A95G variant to exhibit a similar trend with the related glycolate oxidase in electron acceptor substrate specificities, despite the latter containing an alanine at the analogous position.
- Stoisser, Thomas,Rainer, Daniela,Leitgeb, Stefan,Wilson, David K.,Nidetzky, Bernd
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p. 562 - 578
(2015/02/05)
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- Cationic Ir/Me-BIPAM-catalyzed asymmetric intramolecular direct hydroarylation of α-ketoamides
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Asymmetric intramolecular direct hydroarylation of α-ketoamides gives various types of optically active 3-substituted 3-hydroxy-2-oxindoles in high yields with complete regioselectivity and high enantioselectivities (84-98 % ee). This is realized by the use of the cationic iridium complex [Ir(cod) 2](BArF4) and the chiral O-linked bidentate phosphoramidite (R,R)-Me-BIPAM. Carbon's got a brand new bond: Asymmetric intramolecular direct hydroarylation of α-ketoamides gives various optically active 3-substituted 3-hydroxy-2-oxindoles in high yields with complete regioselectivity and high enantioselectivities. This is realized by the use of an asymmetric cationic iridium complex formed in situ (see Scheme).
- Shirai, Tomohiko,Ito, Hajime,Yamamoto, Yasunori
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supporting information
p. 2658 - 2661
(2014/03/21)
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- Biocatalytic asymmetric synthesis of unnatural amino acids through the cascade transfer of amino groups from primary amines onto keto acids
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Flee to the hills: An unfavorable equilibrium in the amino group transfer between amino acids and keto acids catalyzed by α-transaminases was successfully overcome by coupling with a ω-transaminase reaction as an equilibrium shifter, leading to efficient asymmetric synthesis of diverse unnatural amino acids, including L-tert-leucine and D-phenylglycine. Copyright
- Park, Eul-Soo,Dong, Joo-Young,Shin, Jong-Shik
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p. 3538 - 3542
(2014/01/06)
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- Discovery and characterization of a thermostable D-lactate dehydrogenase from Lactobacillus jensenii through genome mining
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The demand on thermostable D-lactate dehydrogenases (d-LDH) has been increased for d-lactic acid production but thermostable d-DLHs with industrially applicable activity were not much explored. To identify a thermostable d-LDH, three d-LDHs from different Lactobacillus jensenii strains were screened by genome mining and then expressed in Escherichia coli. One of the three d-LDHs (d-LDH3) exhibited higher optimal reaction temperature (50 °C) than the others. The T5010 value of this thermostable d-LDH3 was 48.3 °C, much higher than the T5010 values of the others (42.7 and 42.9 °C) and that of a commercial D-lactate dehydrogenase (41.2 °C). The Tm values were 48.6, 45.7 and 55.7 °C for the three d-LDHs, respectively. In addition, kinetic parameter (k cat/Km) of d-LDH3 for pyruvate reduction was estimated to be almost 150 times higher than that for lactate oxidation at pH 8.0 and 25 °C, implying that D-lactate production from pyruvate is highly favored. These superior thermal and kinetic features would make the d-LDH3 characterized in this study a good candidate for the microbial production of D-lactate at high temperature from glucose if it is genetically introduced to lactate producing microbial.
- Jun, Chanha,Sa, Young Seung,Gu, Sol-A,Joo, Jeong Chan,Kim, Seil,Kim, Kyung-Jin,Kim, Yong Hwan
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p. 109 - 117
(2013/04/10)
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- Characterization of d-amino acid aminotransferase from Lactobacillus salivarius
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We searched a UniProt database of lactic acid bacteria in an effort to identify d-amino acid metabolizing enzymes other than alanine racemase. We found a d-amino acid aminotransferase (d-AAT) homologous gene (UniProt ID: Q1WRM6) in the genome of Lactobacillus salivarius. The gene was then expressed in Escherichia coli, and its product exhibited transaminase activity between d-alanine and α-ketoglutarate. This is the first characterization of a d-AAT from a lactic acid bacterium. L. salivarius d-AAT is a homodimer that uses pyridoxal-5′-phosphate (PLP) as a cofactor; it contains 0.91 molecules of PLP per subunit. Maximum activity was seen at a temperature of 60 °C and a pH of 6.0. However, the enzyme lost no activity when incubated for 30 min at 30 °C and pH 5.5 to 9.5, and retained half its activity when incubated at pH 4.5 or 11.0 under the same conditions. Double reciprocal plots of the initial velocity and d-alanine concentrations in the presence of several fixed concentrations of α-ketoglutarate gave a series of parallel lines, which is consistent with a Ping-Pong mechanism. The Km values for d-alanine and α-ketoglutarate were 1.05 and 3.78 mM, respectively. With this enzyme, d-allo-isoleucine exhibited greater relative activity than d-alanine as the amino donor, while α-ketobutylate, glyoxylate and indole-3-pyruvate were all more preferable amino acceptors than α-ketoglutarate. The substrate specificity of L. salivarius d-AAT thus differs greatly from those of the other d-AATs so far reported.
- Kobayashi, Jyumpei,Shimizu, Yasuhiro,Mutaguchi, Yuta,Doi, Katsumi,Ohshima, Toshihisa
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- Deracemization of unnatural amino acid: Homoalanine using d-amino acid oxidase and ω-transaminase
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A deracemization method was developed to generate optically pure l-homoalanine from racemic homoalanine using d-amino acid oxidase and ω-transaminase. A whole cell reaction using a biphasic system converted 500 mM racemic homoalanine to 485 mM l-homoalanine (>99% ee). The Royal Society of Chemistry 2012.
- Seo, Young-Man,Mathew, Sam,Bea, Han-Seop,Khang, Yong-Ho,Lee, Sang-Hyeup,Kim, Byung-Gee,Yun, Hyungdon
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body text
p. 2482 - 2485
(2012/04/23)
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- Mechanistic studies of 1-aminocyclopropane-1-carboxylate deaminase: Characterization of an unusual pyridoxal 5′-phosphate-dependent reaction
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1-Aminocyclopropane-1-carboxylic acid (ACC) deaminase (ACCD) is a pyridoxal 5′-phosphate (PLP)-dependent enzyme that cleaves the cyclopropane ring of ACC, to give α-ketobutyric acid and ammonia as products. The cleavage of the Cα-Cβ bond of an amino acid substrate is a rare event in PLP-dependent enzyme catalysis. Potential chemical mechanisms involving nucleophile- or acid-catalyzed cyclopropane ring opening have been proposed for the unusual transformation catalyzed by ACCD, but the actual mode of cyclopropane ring cleavage remains obscure. In this report, we aim to elucidate the mechanistic features of ACCD catalysis by investigating the kinetic properties of ACCD from Pseudomonas sp. ACP and several of its mutant enzymes. Our studies suggest that the pKa of the conserved active site residue, Tyr294, is lowered by a hydrogen bonding interaction with a second conserved residue, Tyr268. This allows Tyr294 to deprotonate the incoming amino group of ACC to initiate the aldimine exchange reaction between ACC and the PLP coenzyme and also likely helps to activate Tyr294 for a role as a nucleophile to attack and cleave the cyclopropane ring of the substrate. In addition, solvent kinetic isotope effect (KIE), proton inventory, and 13C KIE studies of the wild type enzyme suggest that the Cα-C β bond cleavage step in the chemical mechanism is at least partially rate-limiting under kcat/Km conditions and is likely preceded in the mechanism by a partially rate-limiting step involving the conversion of a stable gem-diamine intermediate into a reactive external aldimine intermediate that is poised for cyclopropane ring cleavage. When viewed within the context of previous mechanistic and structural studies of ACCD enzymes, our studies are most consistent with a mode of cyclopropane ring cleavage involving nucleophilic catalysis by Tyr294.
- Thibodeaux, Christopher J.,Liu, Hung-Wen
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experimental part
p. 1950 - 1962
(2012/03/26)
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- Product-assisted catalysis as the basis of the reaction specificity of threonine synthase
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Threonine synthase (TS), which is a pyridoxal 5′-phosphate (PLP)-dependent enzyme, catalyzes the elimination of the γ-phosphate group from O-phospho-L-homoserine (OPHS) and the subsequent addition of water at Cβ to form L-threonine. The catalytic course of TS is the most complex among the PLP enzymes, and it is an intriguing problem how the elementary steps are controlled in TS to carry out selective reactions. When L-vinylglycine was added to Thermus thermophilus HB8 TS in the presence of phosphate, L-threonine was formed with kcat and reaction specificity comparable with those when OPHS was used as the substrate. However, in the absence of phosphate or when sulfate was used in place of phosphate, only the side reaction product, α-ketobutyrate, was formed. Global analysis of the spectral changes in the reaction of TS with L-threonine showed that compared with the more acidic sulfate ion, the phosphate ion decreased the energy levels of the transition states of the addition of water at the Cβ of the PLP-α-aminocrotonate aldimine (AC) and the transaldimination to form L-threonine. The x-ray crystallographic analysis of TS complexed with an analog for AC gave a distinct electron density assigned to the phosphate ion derived from the solvent near the Cβ of the analog. These results indicated that the phosphate ion released from OPHS by γ-elimination acts as the base catalyst for the addition of water at Cβ of AC, thereby providing the basis of the reaction specificity. The phosphate ion is also considered to accelerate the protonation/ deprotonation at Cγ.
- Murakawa, Takeshi,Machida, Yasuhiro,Hayashi, Hideyuki
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experimental part
p. 2774 - 2784
(2012/01/31)
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- Cytotoxic effect of amide derivatives of trifluoromethionine against the enteric protozoan parasite Entamoeba histolytica
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Amoebiasis, caused by infection with the enteric protist Entamoeba histolytica, is one of the major parasitic diseases. Although metronidazole and its derivatives are currently employed in therapy, the paucity of effective drugs and potential clinical resistance necessitate the development of a novel drug. Trifluoromethionine (TFM) is a promising lead compound for antiamoebic drugs. To potentiate the antiamoebic effect of TFM, we synthesised various amide derivatives of TFM and evaluated their cytotoxicity. The amide derivatives of TFM were observed to have a superior cytotoxic effect compared with TFM and metronidazole against E. histolytica in vitro. Although TFM showed cytotoxicity following degradation by methionine γ-lyase, the derivatives were degraded by the enzyme less efficiently compared with TFM. We further demonstrated that a representative derivative was hydrolysed by the amoebic cell lysate to first yield TFM, followed by degradation similar to TFM. Hydrolysis was partially inhibited by protease inhibitors. A single subcutaneous or oral administration of TFM and its amide derivatives also effectively prevented the formation of amoebic liver abscess in a rodent model. These data demonstrate the improved effectiveness of TFM derivatives against E. histolytica infection and elucidate the mechanisms underlining the mode of action of these compounds.
- Sato, Dan,Kobayashi, Seiki,Yasui, Hiroyuki,Shibata, Norio,Toru, Takeshi,Yamamoto, Masaichi,Tokoro, Gensuke,Ali, Vahab,Soga, Tomoyoshi,Takeuchi, Tsutomu,Suematsu, Makoto,Nozaki, Tomoyoshi
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experimental part
p. 56 - 61
(2012/01/04)
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- PROCESS FOR STRAIGHTENING KERATIN FIBRES WITH A HEATING MEANS AND DENATURING AGENTS
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The invention relates to a process for straightening keratin fibres, comprising: (i) a step in which a straightening composition containing at least two denaturing agents is applied to the keratin fibres, (ii) a step in which the temperature of the keratin fibres is raised, using a heating means, to a temperature of between 110 and 250° C.
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- One-pot conversion of L -threonine into L -homoalanine: Biocatalytic production of an unnatural amino acid from a natural one
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A novel biocatalytic process for production of L-homoalanine from L-threonine has been developed using coupled enzyme reactions consisting of a threonine deaminase (TD) and an ω-transaminase (ω-TA). TD catalyzes the dehydration/deamination of L-threonine, leading to the generation of 2-oxobutyrate which is asymmetrically converted to L-homoalanine via transamination with benzylamine executed by ω-TA. To make up the coupled reaction system, we cloned and overexpressed a TD from Escherichia coli and an (S)-specific ω-TA from Paracoccus denitrificans. In the coupled reactions, L-threonine serves as a precursor of 2-oxobutyrate for the ω-TA reaction, eliminating the need for employing the expensive oxo acid as a starting reactant. In contrast to α-transaminase reactions in which use of amino acids as an exclusive amino donor limits complete conversion, amines are exploited in the ω-TA reaction and thus maximum conversion could reach 100%. The ω-TA-only reaction with 10 mM 2-oxobutyrate and 20 mM benzylamine resulted in 94% yield of optically pure L-homoalanine (ee>99%). However, the ω-TA-only reaction did not produce any detectable amount of L-homoalanine from 10 mM L-threonine and 20 mM benzylamine, whereas the ω-TA reaction coupled with TD led to 91% conversion of L-threonine to L-homoalanine. Copyright
- Park, Eulsoo,Kim, Minji,Shin, Jong-Shik
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scheme or table
p. 3391 - 3398
(2011/02/23)
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- Characterization of two isotypes of l-threonine dehydratase from Entamoeba histolytica
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The genome sequence of the enteric protozoan parasite Entamoeba histolytica suggests that amino acid catabolism plays an important role in energy metabolism. In the present study, we described kinetic and regulatory properties of catabolic l-threonine and l-serine dehydratase (TD) from E. histolytica. TD catalyses the pyridoxal phosphate-dependent dehydrative deamination of l-threonine and l-serine to ammonia and keto acids (2-oxobutyrate and pyruvate, respectively). E. histolytica possesses two TD isotypes (EhTD1-2) showing 38% mutual identity, a calculated molecular mass of 45.0 or 46.5 kDa, and an isoelectric point of 6.68 or 5.88, respectively. Only EhTD1 showed l-threonine and l-serine dehydrative deaminating activities whereas EhTD2, in which the amino acid residues involved in the substrate and cofactor binding were not conserved, was devoid of these activities. The kcat/Km value of EhTD1 was >3 fold higher for l-threonine than l-serine. EhTD1 was inhibited by l-cysteine in a competitive manner with the Ki values of 1.1 mM and 2.2 mM for l-serine and l-threonine, respectively. EhTD1 was insensitive to the allosteric activation by AMP or CMP. Three major substitutions of EhTD1 likely attribute to the insensitivity. EhTD1 was also inhibited about 50% by 20 mM 2-oxobutyrate, pyruvate, and glyoxylate; the inhibition was not, however, reversed by AMP. Together, these data showed that EhTD1 possesses unique regulatory properties distinct from other organisms and may play an important role in energy metabolism via amino acid degradation in E. histolytica.
- Husain, Afzal,Jeelani, Ghulam,Sato, Dan,Ali, Vahab,Nozaki, Tomoyoshi
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scheme or table
p. 100 - 104
(2011/10/13)
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- METHOD FOR SYNTHESIS OF KETO ACID OR AMINO ACID BY HYDRATION OF ACETHYLENE COMPOUND
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An object of the present invention is to provide a method for synthesis of keto acids by hydration of an acetylene compound (acetylene-carboxylic acids) under mild conditions free from harmful mercury catalysts and a method for synthesis of amino acids from acetylene-carboxylic acids in a single container (one-pot or tandem synthesis). In one embodiment of the method according to the present invention for synthesis of keto acids, acetylene-carboxylic acids is hydrated in the presence of a metal salt represented by General Formula (1), where M1 represents an element in Group VIII, IX, or X of the periodic table, and X1, X2, or X3 ligand represents halogen, H2O, or a solvent molecule, and k represents a valence of a cation species, and Y represents an anion species, and L represents a valence of the anion species, and each of K and L independently represents 1 or 2, and k × m = L × n.
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Page/Page column 18; 19; 20; 21; 25; 26-27
(2008/12/06)
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- Method for preparing chiral diphosphines
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The invention concerns a method for preparing a compound of formula (1) wherein: A represents naphthyl or phenyl optionally substituted; and Ar1, Ar2independently represent a saturated or aromatic carbocyclic group, optionally substituted.
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- Method and product for skin lightening
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A method and cosmetic product for lightening skin is provided, the method including wiping the skin with a cosmetic towelette. Impregnated on the towelette is an alpha-hydroxy carboxylic acid or salt thereof and a sunscreen agent.
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- Towelette product
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A disposable towelette product is provided which includes a flexible water-insoluble substrate such as a tissue impregnated with an alpha- or beta-hydroxycarboxylic acid in a cosmetically acceptable carrier vehicle. Impregnated cosmetic composition in water will have a pH no higher than 6.8. A silicone microemulsion is present to minimize any stickiness resulting from deposition of the hydroxycarboxylic acid by the towelette onto the skin. In the presence of fatty acid group containing surfactants, the silicone microemulsion controls foul odors that the surfactants may emit through hydrolysis at low pH.
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- Towelette product for minimizing facial fine lines and wrinkles
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A disposable towelette is provided which includes a flexible substrate such as a cellulosic tissue impregnated with an alpha-hydroxycarboxylic add delivered in a cosmetically acceptable carrier vehicle. There is further provided a method for cleansing skin and simultaneously inhibiting fine lines and wrinkles by wiping the skin with the impregnated towelette.
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- Asymmetric hydrogenation method of a ketonic compound and derivative
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The present invention relates to a process for the asymmetric hydrogenation of a ketonic compound and derivative. The invention relates to the use of optically active metal complexes as catalysts for the asymmetric hydrogenation of a ketonic compound and derivative. The process for the asymmetric hydrogenation of a ketonic compound and derivative is characterized in that the asymmetric hydrogenation of said compound is carried out in the presence of an effective amount of a metal complex comprising as ligand an optically active diphosphine corresponding to one of the following formulae: STR1
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- Enzymatic Resolution of Chiral 2-Hydroxy Carboxylic Acids by Enantioselective Oxidation with Molecular Oxygen Catalyzed by the Glycolate Oxidase from Spinach (Spinacia oleracea)
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The enzymatic oxidation of a variety of saturated and unsaturated aliphatic derivatives of racemic 2-hydroxy acids 1 to their 2-oxo acids 2 with molecular oxygen catalyzed by the glycolate oxidase from spinach (Spinacia oleracea) was shown to proceed highly enantioselectively.Thus, the glycolate oxidase-catalyzed kinetic resolution provides a convenient biocatalytic method for the preparation of enantiomerically pure (R)-2-hydroxy acids.The absolute configuration of the (R)-2-hydroxy acid 1b assigned by comparison of the measured optical rotation value with that of the literature data and by application of the exciton-coupled circular dichroism method (ECCD) on its bichromophoric 2-naphthoate 9-methylanthryl derivative 3b.These results establish the ECCD method as a convenient microscale chirooptic tool for the configurational assignment of 2-hydroxy acids.
- Adam, Waldemar,Lazarus, Michael,Boss, Barbara,Saha-Moeller, Chantu R.,Humpf, Hans-Ulrich,Schreier, Peter
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p. 7841 - 7843
(2007/10/03)
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- Concerted base-promoted elimination in the decomposition of N-halo amino acids
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N-Chloroamino acids are unstable in aqueous solution and decompose through different pathways depending on the reaction conditions, yielding precursors of carcinogenic and/or mutagenic compounds. One of these pathways is a 1,2-elimination process, which has scarcely received any attention and for which no systematic analysis is available. The process is first order relative to the N-chloroamino acid and to that of hydroxide ion. The use of 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoropropan-2-ol buffer solutions established that the process is general-base catalysed. The reaction rate is affected by the presence of a methyl group on the nitrogen atom and the nature of the leaving group. The results show an important steric effect due to the alkyl substituents on the α-carbon. With bulky alkyl substitueras on the α-carbon, and in particular in the case of N-alkylamino acids, the catalytic effect increases as the base strength decreases. To characterize the transition state, Brtonsted's β and βlg were used. A More O'Ferrall-Jencks diagram shows the transition state structure changing from carbanion-like to nitrenium-like, a large perpendicular effect being evident. The reaction proceeds through a concerted mechanism AxhDHDN instead of the stepwise AxhDH? + DN proposed earlier.
- Armesto,Canle L,Garcia,Losada,Santaballa
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p. 552 - 560
(2007/10/03)
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- Structures of puwainaphycins A-E
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Puwainaphycins A-E, one of which (C) is a potent cardioactive agent in isolated mouse atria, are cyclic decapeptides that have beeen isolated from a terrestrial blue-green alga Annabaena sp. BQ-16-1. The structures of puwainaphycins A-E, including most of the stereochemical features, have been elucidated by a combination of spectral and chemical methods.
- Gregson, John M.,Chen, Jian-Lu,Patterson, Gregory M. L.,Moore, Richard E.
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p. 3727 - 3734
(2007/10/02)
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- Microbial Production of 2-Oxobutyric Acid from Crotonic Acid
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2-Oxobutyric acid (OBA) was produced from crotonic acid by two steps.OBA was produced from threo-(+/-)-dihydroxybutyric acid ((2RS,3SR)-2,3-dihydroxybutyric acid, DHB) by the action of cells of Pseudomonas putida.DHB is easily prepared by oxidation of crotonic acid with N-methylmorpholine-N-oxide.The microorganism was screened from a soil sample as the best producer of OBA, although the strain could not assimilate DHB as a sole carbon source.The culture conditions of the microorganism and the reaction conditions were optimized.In the presence of 80 g/l of the cells of P. putida, the amount of OBA produced from DHB was 4.8 g/l under the best conditions examined, with a molar yield of 47 percent.
- Furuyoshi, Setsuo,Nawa, Yoshito,Kawabata, Nariyoshi
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p. 123 - 128
(2007/10/02)
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- An Evaluation of the Substrate Specificity, and of Its Modification by Site-Directed Mutagenesis, of the Cloned L-Lactate Dehydrogenase from Bacillus stearothermophilus
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The L-lactate dehydrogenase of Bacillus stearothermophilus (BSLDH) is a stable, thermophilic oxidoreductase.It has been selected as a model of enzymes with considerable future promise in assymetric synthesis in that it has been cloned to ensure a plentiful and inexpensive supply and because of the potential for tailoring its specificity to accept unnatural substrate structures via the site-directed mutagenesis techniques of moleculer biology.In this study, the specificity of BSLDH toward representative α-keto acids possessing straight- and branched-chain alkyl,cycloalkyl, or aromatic side chains has been evaluated.The results show that substrates that are sterically bulky in the region of the α-keto group to be reduced are poorly accepted by the enzyme.Graphics analyses indicated that the low activities of these hindered substrates might be partly due to a bad interaction of the active site residue Gln102 with large or branched substituents adjacent to the α-keto group.Accordingly, Gln102 has been replaced by the smaller Asn residue by site-directed mutagenesis in an attempt to expand the active site volume available to receive substrates larger than the natural pyruvate.However, the kinetic data show that bulky α-keto acids are only marginally better accommodated by the Gln102 -> Asn mutant than by the wild-type enzyme.
- Luyten, Marcel A.,Bur, Daniel,Wynn, Hla,Parris, Wendy,Glod, Marvin,et al.
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p. 6800 - 6804
(2007/10/02)
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- Uncatalyzed and Chorismate Mutase Catalyzed Claisen Rearrangement of (Z)-9-Methylchorismic Acid
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A synthesis of (-)- and (+/-)-(Z)-9-methylchorismic acid (3) is reported.The half-life for the uncatalyzed Claisen rearrangement of (+/-)-3 in H2O (pH 7.5, 30 deg C) is 5.7 h.Chorismate analogue (-)-3 was a modest substrate for chorismate mutase (chorismate mutase-prephenate dehydrogenase from E. coli): Km = 4.0 mM, kcat./kuncat. = 4.2*104.It was established that the enzyme-catalyzed Claisen rearrangement of (-)-3 proceeds through a chairlike transition state in similar fashion to the chorismate mutase catalyzed rearrangement of (-)-chorismic acid (1).
- Lesuisse, Dominique,Berchtold, Glenn A.
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p. 4992 - 4997
(2007/10/02)
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- Process for preparing α-keto-carboxylic acids from acyl halides
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A process for the production of α-keto-carboxylic acids of the general formula: STR1 wherein R1 and R2 are the same or different and are hydrogen, hydrocarbyl radicals, substituted hydrocarbyl radicals or hydrocarbyloxy radicals by reacting an acyl halide of the formula: STR2 wherein R1 and R2 are as defined above and X represents halogen, in a liquid solvent medium, with an alkali metal tetracarbonyl cobaltate complex of the formula: wherein M is an alkali metal to form the corresponding acylcobaltcarbonyl complex of the formula: STR3 wherein R1 and R2 are as defined above, reacting the acylcobaltcarbonyl complex thus formed with carbon monoxide and an alkali metal hydroxide or an alkaline earth metal hydroxide at elevated temperature and elevated pressure in a liquid solvent medium to form the corresponding alkali metal salt or alkaline earth metal salt of the product α-keto-carboxylic acid and thereafter acidifying the salt of the α-keto-carboxylic acid to form the product α-keto-carboxylic acid.
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- Preparation of α-keto-carboxylic acids from acyl halides
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A process for the production of α-keto-carboxylic acids of the general formula: STR1 wherein R1 and R2 are the same or different and are hydrogen, hydrocarbyl radicals, substituted hydrocarbyl radicals or hydrocarbyloxy radicals by reacting an acyl halide of the formula: STR2 wherein R1 and R2 are as defined above and X represents halogen, in a liquid solvent medium, with an alkali metal tricarbonyl[triphenylphosphine]cobaltate complex of the formula: wherein M is an alkali metal to form the corresponding phenylacetyl tricarbonyl[triphenylphosphine]cobalt complex of the formula: STR3 wherein R1 and R2 are as defined above, reacting the acylcobaltcarbonyl complex thus formed with carbon monoxide and an alkali metal hydroxide or an alkaline earth metal hydroxide at elevated temperature and elevated pressure in a liquid solvent medium to form the corresponding alkali metal salt or alkaline earth metal salt of the product α-keto-carboxylic acid and thereafter acidifying the salt of the α-keto-carboxylic acid to form the product α-keto-carboxylic acid.
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- Pyridoxamine and 2-Oxalopropionic Acid in Aqueous Systems: Conditional Imine Formation Constants and Rate Constants of Vitamin B6 Catalyzed Decarboxylation
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The conditional Schiff base formation constants (Kc) of pyridoxamine (PM) and 2-oxalopropionic acid (OPA) were determined spectrophotometrically in basis aqueous solutions.These equilibrium constants exhibit pH dependence with maximum ketimine formation occuring near pH 9.0 (Kc = 9.6).The kinetics of vitamin B6 catalyzed decarboxylation of OPA have been studied spectrophometrically, and the observed rate constant of decarboxylation (kobsd) exhibited pH dependence with the maximum occuring at approximatly the pH corresponding to maximum ketimine formation (kobsd = 15.6 * 10-4 s-1 at 1.01 * 10-4 M OPA and 1.00 * 10-5 M PM).Microscopic rate constants (kSB) for the decarboxylation of the Schiff base species present in solution also showed pH dependence with the greatest catalytic activity at pH 7.0 (kSB = 38.4 s-1) and the least at pH 12.47 (kSB = 0.2 s-1).The relative magnitudes of the kSB's determined are discussed in terms of the various protonated forms of the OPA:PM ketimine,and the corresponding pKa's have been estimated from the rate constant-pH profiles.
- Kubala, Gregory,Martell, Arthur E.
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p. 449 - 455
(2007/10/02)
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- Kinetics and mechanism of the cerium(IV) oxidation of methylmalonic acid and of ethylmalonic acid in acid media
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The kinetics and mechanism of the oxidation of methylmalonic acid and of ethylmalonic acid by cerium(IV) in acid media was studied with use of the stopped-flow technique. The observed rate law was found to be of the form -d[Ce(IV)]/dt = kH[Ce(IV)][RCH(CO2H)2]. The second-order rate constant, kH, was found to be hydrogen ion dependent and of the form kH = (k[H+]2 + k′[H+] + k″)/([H+] + K). A mechanism consistent with these results is proposed.
- Tischler, Frances,Morrow, Jack I.
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p. 2286 - 2289
(2008/10/08)
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- Biosynthetic Threonine Deaminase from Proteus morganii
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Biosynthetic threonine deaminase was purified to an apparent homogeneous state from the cell extract of Proteus morganii, with an overall yield of 7.5percent.The enzyme had s20,w0 of 10.0 S, and the molecular weight was calculated to be approximately, 228,000.The molecular weight of a subunit of the enzyme was estimated to be 58,000 by sodium dodecyl sulfate gel electrophoresis.The enzyme seemed to have a tetrameric structure consisting of identical subunits.The enzyme had a marked yellow color with an absorption maximum at 415 nm and contained 2 mol of pyridoxal 5'-phosphate per mol.The threonine deaminase catalyzed the deamination of L-threonine, L-serine, L-cysteine and β-chloro-L-alanine.Km values for L-threonine and L-serine were 3.2 and 7.1 mM, respectively.The enzyme was not activated by AMP, ADP and ATP, but was inhibited by L-isoleucine.The Ki for L-isoleucine was 1.17 mM, and the inhibition was not recovered by L-valine.Treatment with mercuric chloride effectively protected the enzyme from inhibition by L-isoleucine.
- Yoshida, Hajime,Hanada, Keizo,Ohsawa, Hisakazu,Kumagai, Hidehiko,Yamada, Hideaki
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p. 1035 - 1042
(2007/10/02)
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- Kinetics and Mechanism of Oxidation of Glycollic, Lactic and α-Hydroxybutyric Acids by Sodium N-Chlorobenzenesulphonamide
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The oxidation of glycollic, lactic and α-hydroxybutyric acids by sodium N-chlorobenzenesulphonamide (chloramine-B, CAB) in aqueous acid solution yields the corresponding aldo- or ketoacid as the main product.The reaction rates are first order with respect to the oxidant, the hydroxy acid and acidity.The oxidation of α,α-dideuterioglycollic acid indicates a kinetic isotope effect, kH/kD = 3.96 +/- 0.07 at 303 K.The solvent isotope effect, k(H2O)/k(D2O) = 0.41 at 303 K.The rate increases with the introduction of alkyl group in the hydroxy acid molecule.Themost probable oxidising species is PhSO2NHCl.A mechanism involving transfer of a hydride ion to the oxidant is proposed.
- Mathur, Anil K.,Banerji, Kalyan K.
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p. 529 - 530
(2007/10/02)
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- OXIDATION OF 3,4-DISUBSTITUTED ISOXAZOLIN-5-ONES. A NEW SYNTHESIS OF α-KETO ACIDS
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m-Chloroperoxybenzoic or peroxyformic acid oxidation of 3,4-disubstituted isoxazolin-5-ones affords the corresponding 4-hydroxy derivatives from which, by ring opening, nitriles and α-keto acids are obtained.
- Baldoli, Clara,Beccalli, Egle M.,Licandro, Emanuela,Marchesini, Alessandro
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p. 347 - 350
(2007/10/02)
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- Reaction Kinetics and Equilibria of β-Elimination of Some Schiff Base Complexes
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The kinetics of β-elimination of O-phosphoserine, β-chloroalanine, S-ethylcysteine, and β-chloro-α-aminobutyric acid was investigated by NMR in deuterium oxide media at 31.5 +/- 0.5 deg C in the presence of pyridoxal and in the presence and the absence of Ga(III), Al(III), and Zn(II) ions.The reaction rate constants and relevant equilibrium constants are reported for these systems.The specific rate constants for the individual molecular species in solution were determined from the observed reaction rate cobstants and equilibrium constants applicable to these systems.Catalysis by pyridoxal in the absence of metal ions showed an increase in rate as pD was increased, with a rate maximum in the region of pD 8-9, and moderate decrease at higher pH.The first-order rate constants varied with the amino acid moiety in the order β-chloroalanine > O-phosphoserine > β-chloro-α-aminobutyric acid > S-ethylcysteine.The rate constants reported for pyridoxal catalysis in the presence of metal ions show rate enhancements in the order of ten times the values of metal-free systems.Possible mechanisms of these reactions are discussed.
- Tatsumoto, Kuniyasu,Martell, Arthur E.,Motekaitis, Ramunas J.
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p. 6197 - 6203
(2007/10/02)
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