Xn:Harmful;
88-75-5Relevant articles and documents
Selective Nitration of Phenol
Pervez, Humayun,Rees, Lilias,Suckling, Colin J.
, p. 512 - 513 (1985)
Activated nitro derivatives of pyridinium salts have been shown to mediate in the highly selective ortho nitration of phenol in high yield.
The catalytic properties and stability of β-galactosidases from fungi
Pilipenko,Atyaksheva,Poltorak,Chukhrai
, p. 2250 - 2254 (2008)
The catalytic activity of β-galactosidases from fungi Penicillium canescens and Aspergillus oryzae is maximum in a weakly acidic medium and does not depend on the presence of magnesium cations in the reaction medium. The enzyme from Aspergillus oryzae fungi is more active, and that from Penicillium canescens is stabler. One of stability indications is the presence of an induction period in the kinetic curves of thermal inactivation. This period disappears at 54°C for the enzyme from Aspergillus oryzae and at 59°C for the enzyme from Penicillium canescens. The temperature dependences of the effective rate constants for the inactivation of the tetrameric enzyme from Penicillium canescens show that the main reason for enzyme inactivation is the dissociation of oligomeric forms below 66°C (E act = 85 kJ/mol) and enzyme denaturation at higher temperatures (E act = 480 kJ/mol). The dissociation stage is absent for monomeric β-galactosidase from Aspergillus oryzae fungi, and the activation energy of inactivation is 450 kJ/mol over the whole temperature range studied (53-60°C). Pleiades Publishing, Ltd., 2008.
Enhanced catalytic and antibacterial activities of silver nanoparticles immobilized on poly(N-vinyl pyrrolidone)-grafted graphene oxide
Singh, Shikha,Gundampati, Ravi Kumar,Mitra, Kheyanath,Ramesh,Jagannadham, Medicherla V.,Misra, Nira,Ray, Biswajit
, p. 81994 - 82004 (2015)
Poly(N-vinyl pyrrolidone) (PNVP)-grafted graphene oxide (GO) (GO-PNVP) has been synthesized using a GO-based macro-RAFT agent prepared via click reaction of alkyne-terminated RAFT agent (S)-2-(propynyl propionate)-(o-ethyl xanthate) and azide-functionalized GO (GO-N3). FTIR, XPS, Raman, TGA and DSC studies confirmed its formation. Silver nanoparticles are then immobilized on GO-PNVP and GO via in situ reduction of silver nitrate in the presence and absence of glucose at 40 and 95 °C, respectively. FT-IR, UV-Vis, XRD, SEM and TGA studies supported the incorporation of silver (Ag) nanoparticles. Ag nanoparticles immobilized on GO-PNVP are small, spherical and narrowly distributed (homogenous, monodisperse) compared to GO. These nanocomposites are explored as catalysts for the reduction of p-nitrophenol into p-aminophenol and also as antibacterial agents towards Gram(+) S. aureus and Gram(-) E. coli bacteria. Ag nanoparticle immobilized GO-PNVP showed efficient catalytic activity and excellent reusability along with an excellent antibacterial activity. Hence, grafting of PNVP enhances the catalytic and antibacterial properties of GO.
Improving the properties of β-galactosidase from Aspergillus oryzae via encapsulation in aggregated silica nanoparticles
Wu, Zhuofu,Wang, Zhi,Guan, Buyuan,Wang, Xue,Zhang, Ye,Xiao, Yu,Zhi, Bo,Liu, Yunling,Li, Zhengqiang,Huo, Qisheng
, p. 3793 - 3797 (2013)
In this study, a new immobilization method was exploited to encapsulate β-galactosidase (β-gal) from Aspergillus oryzae using aggregated core-shell silica nanoparticles as a matrix. Transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the material encapsulated β-gal. Compared to the free β-gal, the encapsulated β-gal shows a broader pH tolerance and thermal stability. Furthermore, the encapsulated β-gal shows better storage stability over 30 days. After nine cycles of hydrolytic reaction, the encapsulated β-gal still maintains 94.2% of its initial activity, which indicates that the β-gal exhibits excellent reusability after encapsulation.
Role of lysine ε-amino groups of β-lactoglobulin on its activating effect of Kluyveromyces lactis β-galactosidase
Del Moral-Ramirez, Elizabeth,Dominguez-Ramirez, Lenin,Cruz-Guerrero, Alma E.,Rodriguez-Serrano, Gabriela M.,Garcia-Garibay, Mariano,Gomez-Ruiz, Lorena,Jimenez-Guzman, Judith
, p. 5859 - 5863 (2008)
Native β-lactoglobulin binds and increases the activity of Kluyveromyces lactis β-galactosidase. Construction of a three-dimensional (3D) model of β-lactoglobulin showed that lysine residues 15, 47, 69, and 138 are the most exposed ones, thus the ones more likely to interact with β-galactosidase. Molecular docking estimated the interaction energies of amino acid residues with either lactose or succinic anhydride, showing that Lys138 is the most likely to react with both. Affinity chromatography demonstrated that succinylated β-lactoglobulin diminished its ability to bind to the enzyme. Furthermore, when activity was measured in the presence of succinylated β-lactoglobulin, its activating effect was lost. Since succinylation specifically blocks Lys ε-amino groups, their loss very likely causes the disappearance of the activating effect. Results show that the activating effect of β-lactoglobulin on β-galactosidase activity is due to the interaction between both proteins and that this interaction is very likely to occur through the Lys ε-amino groups of β-lactoglobulin.
A novel cold-active β-D-galactosidase with transglycosylation activity from the Antarctic Arthrobacter sp. 32cB - Gene cloning, purification and characterization
Pawlak-Szukalska, Anna,Wanarska, Marta,Popinigis, Arkadiusz Tomasz,Kur, Józef
, p. 2122 - 2133 (2014)
A gene encoding a novel β-d-galactosidase from the psychrotolerant Antarctic bacterium Arthrobacter sp. 32cB was isolated, cloned and expressed in Escherichia coli. The active form of recombinant β-d-galactosidase consists of two subunits with a combined molecular weight of approximately 257 kDa. The enzyme's maximum activity towards o-nitrophenyl-β-d-galactopyranoside was determined as occurring at 28 °C and pH 8.0. However, it exhibited 42% of maximum activity at 10°C and was capable of hydrolyzing both lactose and o-nitrophenyl-β-d-galactopyranoside at that temperature, with Km values of 1.52 and 16.56 mM, and kcat values 30.55 and 31.84 s-1, respectively. Two units of the enzyme hydrolyzed 90% of the lactose in 1 mL of milk at 10°C in 24 h. The transglycosylation activity of Arthrobacter sp. 32cB β-d-galactosidase was also examined. It synthesized galactooligosaccharides in a temperature range from 10 to 30°C. Moreover, it catalyzed the synthesis of heterooligosaccharides such as lactulose, galactosyl-xylose and galactosyl-arabinose, alkyl glycosides, and glycosylated salicin from lactose and the appropriate acceptor at 30°C. The properties of Arthrobacter sp. 32cB β-d-galactosidase make it a candidate for use in the industrial removal of lactose from milk and a promising tool for the glycosylation of various acceptors, especially those which are thermosensitive.
β-galactosidase from Lactobacillus plantarum WCFS1: Biochemical characterization and formation of prebiotic galacto-oligosaccharides
Iqbal, Sanaullah,Nguyen, Thu-Ha,Nguyen, Tien Thanh,Maischberger, Thomas,Haltrich, Dietmar
, p. 1408 - 1416 (2010)
Recombinant β-galactosidase from Lactobacillus plantarum WCFS1, homologously over-expressed in L. plantarum, was purified to apparent homogeneity using p-aminobenzyl 1-thio-β-D-galactopyranoside affinity chromatography and subsequently characterized. The enzyme is a heterodimer of the LacLMfamily type, consisting of a small subunit of 35 kDa and a large subunit of 72 kDa. The optimum pH for hydrolysis of its preferred substrates o-nitrophenyl-β-D-galactopyranoside (oNPG) and lactose is 7.5 and 7.0, and optimum temperature for these reactions is 55 and 60 °C, respectively. The enzyme is most stable in the pH range of 6.5-8.0. The Km, k cat and kcat/Km values for oNPG and lactose are 0.9 mM, 92 s-1, 130 mM-1 s-1 and 29 mM, 98 s-1, 3.3 mM-1 s-1, respectively. The L. plantarum β-galactosidase possesses a high transgalactosylation activity and was used for the synthesis of prebiotic galacto-oligosaccharides (GOS). The resulting GOS mixture was analyzed in detail, and major components were identified by using high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) as well as capillary electrophoresis. The maximal GOS yield was 41% (w/w) of total sugars at 85% lactose conversion (600 mM initial lactose concentration). The enzyme showed a strong preference for the formation of β-(1→6) linkages in its transgalactosylation mode, while β-(1→3)-linked products were formed to a lesser extent, comprising ～80% and 9%, respectively, of the newly formed glycosidic linkages in the oligosaccharide mixture at maximum GOS formation. The main individual products formed were β-DGalp-( 1→6)-D-Lac, accounting for 34% of total GOS, and β-D-Galp-(1→6)-D-Glc, making up 29% of total GOS.
Determination of the transgalactosylation activity of Aspergillus oryzae β-galactosidase: Effect of pH, temperature, and galactose and glucose concentrations
Vera, Carlos,Guerrero, Cecilia,Illanes, Andrés
, p. 745 - 752 (2011)
The catalytic potential of β-galactosidase is usually determined by its hydrolytic activity over natural or synthetic substrates. However, this method poorly predicts enzyme behavior when transglycosylation instead of hydrolysis is being performed. A system for determining the transgalactosylation activity of β-galactosidase from Aspergillus oryzae was developed, and its activity was determined under conditions for the synthesis of galacto-oligosaccharides and lactulose. Transgalactosylation activity increased with temperature up to 55 °C while the effect of pH was mild in the range from pH 2.5 to 5.5, decreasing at higher values. The effect of glucose and galactose on transgalactosylation activity was also assessed both in the reactions for the synthesis of galacto-oligosaccharides and lactulose and also in the reaction of hydrolysis of o-nitrophenyl β-d-galactopiranoside. Galactose was a competitive inhibitor and its effect was stronger in the reactions of transgalactosylation than in the reaction of hydrolysis. Glucose was a mild activator of β-galactosidase in the reaction of hydrolysis, but its mechanism of action was more complex in the reactions of transgalactosylation, having this positive effect only at low concentrations while acting as an inhibitor at high concentrations. This information is relevant to properly assess the effect of monosaccharides during the reactions of the synthesis of lactose-derived oligosaccharides, such as galacto-oligosaccharides and lactulose.
Immobilization of β-Galactosidases on Magnetic Nanocellulose: Textural, Morphological, Magnetic, and Catalytic Properties
Gennari, Adriano,Mobayed, Francielle H.,Da Rolt Nervis, Brenda,Benvenutti, Edilson V.,Nicolodi, Sabrina,Da Silveira, Nádya Pesce,Volpato, Giandra,Volken De Souza, Claucia F.
, (2019)
We describe a process for obtaining nanocrystalline cellulose (NC) by either acidic (H-NC) or alkaline treatment (OH-NC) of microcrystalline cellulose, which was subsequently bonded to magnetic nanoparticles (H-NC-MNP and OH-NC-MNP) and used as support for the immobilization of Aspergillus oryzae (H-NC-MNP-Ao and OH-NC-MNP-Ao) and Kluyveromyces lactis (H-NC-MNP-Kl and OH-NC-MNP-Kl) β-galactosidases. The mean size of magnetic nanocellulose particles was approximately 75 nm. All derivatives reached saturation magnetizations of 7-18 emu/g, with a coercivity of approximately 4 kOe. Derivatives could be applied in batch hydrolysis of lactose either in permeate or in cheese whey for 30× and it reached hydrolysis higher than 50%. Furthermore, using a continuous process in a column packed-bed reactor, the derivative OH-NC-MNP-Ao had capacity to hydrolyze over 50% of the lactose present in milk or whey after 24 h of reaction. Fungal β-galactosidases immobilized on magnetic nanocellulose can be applied in lactose hydrolysis using batch or continuous processes.
Lactose hydrolysis by β galactosidase immobilized on concanavalin A-cellulose in batch and continuous mode
Ansari, Shakeel Ahmed,Husain, Qayyum
, p. 68 - 74 (2010)
β Galactosidase from Aspergillus oryzae was immobilized on an inexpensive bioaffinity support, (concanavalin A) Con A-cellulose. The mode of interaction between Con A-cellulose and β galactosidase is shown by Fourier transform infrared spectroscopy. Con A-cellulose adsorbed and crosslinked β galactosidase preparation retained 78% of the initial activity. Soluble and immobilized β galactosidase showed the same pH-optimum at pH 4.6. The temperature-optimum was increased from 50 to 60 °C for the immobilized β galactosidase. The immobilized enzyme had higher thermal stability at 60 °C. The crosslinked adsorbed enzyme retained 80 and 70% of the original enzyme activity in the presence of 3% calcium chloride and 3% galactose, respectively. Moreover, the adsorbed crosslinked and adsorbed β galactosidase exhibited 84 and 75% enzyme activity even after their sixth repeated use, respectively. The crosslinked adsorbed enzyme retained 93% activity after 1 month storage while the native enzyme showed only 63% activity under similar incubation conditions. Immobilized β galactosidase showed higher lactose hydrolysis from solution in batch process at 60 °C as compared to its hydrolysis at 50 °C. The continuous hydrolysis of lactose was appreciably different at various flow rates. Thus, the reactor filled with crosslinked Con A-cellulose adsorbed β galactosidase could be successfully employed for the continuous hydrolysis of lactose from milk and whey.
