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Relevant academic research and scientific papers

Inhibition of xanthine oxidase by theaflavin: Possible mechanism for anti-hyperuricaemia effect in mice

Xanthine oxidase (XO) catalyzes the oxidation of hypoxanthine to xanthine and then to uric acid. Excessive production of uric acid leads to hyperuricaemia. Due to the serious side effects of allopurinol, it is an urgent need to explore new XO inhibitors. Herein, the effects of theaflavin (TF1) on XO and anti-hyperuricaemia effect in hyperuricemic mice were investigated. Kinetic analysis indicate that TF1 is a reversible competitive inhibitor and has a significant inhibitory effect on XO with an IC50 value of 63.17 ± 0.13 μmol/L. Analysis of fluorescence spectra suggests that TF1 causes the obvious fluorescence quenching of XO, which is mainly driven by hydrophobic interactions and hydrogen bonds. Docking studies demonstrate that TF1 interacts with dozens of amino acid residues surrounded in the active cavity of XO, including Glu-879, Pro-1012, Thr-1010, Val-1011, Lys-771, Glu-802, Pro-1076, Leu-873, Leu-1014, Asn-768, Leu-648 and Phe-649. The inhibitory mechanism may be the insertion of TF1 into the active site of XO, which hinders the substrate xanthine to enter into the site. Furthermore, the results from animal experiments demonstrate that TF1 is effective in reducing serum uric acid in mice. These findings suggest that TF1 may be a potential drug candidate for the treatment of hyperuricaemia.

Comprehensive study of bioanalytical platforms: Xanthine oxidase

A comprehensive study of a general bioanalytical platform for biosensor applications is presented using xanthine oxidase (XnOx) as a case study within the framework of developing approaches of broad applicability. In this context, emphasis is placed on amperometric biosensors based on XnOx, which has been immobilized by covalent binding to gold electrodes modified with dithiobis-N-succinimidyl propionate. The immobilized XnOx layers have been characterized using atomic force microscopy under liquid conditions and quartz crystal microbalance techniques. In addition, spatially resolved mapping of enzymatic activity has been carried out using scanning electrochemical microscopy. Redox dyes of phenothiazine derivatives, specifically, thionine and methylene blue, have been found to work well as electron acceptors for reduced XnOx. The kinetic parameters and equilibrium constants of the mediated enzymatic oxidation of xanthine in the presence of the above-mentioned redox dyes have been calculated. The response of the enzymatic electrode to varying xanthine concentrations has been obtained in the presence of thionine or methylene blue as redox mediator in solution. Under these conditions, xanthine could be determined amperometrically at +0.2 V versus SSCE.

Real-Time Monitoring of Human Guanine Deaminase Activity by an Emissive Guanine Analog

Guanine deaminase (GDA) deaminates guanine to xanthine. Despite its significance, the study of human GDA remains limited compared to other metabolic deaminases. As a result, its substrate and inhibitor repertoire are limited, and effective real-time activity, inhibitory, and discovery assays are missing. Herein, we explore two emissive heterocyclic cores, based on thieno[3,4-d]pyrimidine (thN) and isothiazole[4,3-d]pyrimidine (tzN), as surrogate GDA substrates. We demonstrate that, unlike the thieno analog, thGN, the isothiazolo guanine surrogate, tzGN, does undergo effective enzymatic deamination by GDA and yields the spectroscopically distinct xanthine analog, tzXN. Further, we showcase the potential of this fluorescent nucleobase surrogate to provide a visible spectral window for a real-time study of GDA and its inhibition.

Proposed mechanisms for HOOOH formation in two typical enzyme reactions responsible for superoxide anion production in biological systems

We investigated the hypoxanthine (HPX)-xanthine oxidase (XOD) reaction by examining the chemiluminescence (CL) response mediated by a luminol analog, 8-amino-5-chloro-7-phen-y]pyrido[3,4-d]pyridazine-1,4-(2H, 3H)-dione sodium salt (1-012). It was found th

Photosensitized oxidation of hypoxanthine and xanthine by aluminum phthalocyanine tetrasulfonate. Role of the alkylating quinone 2,5-dichloro-diaziridinyl-1,4-benzoquinone

Photoirradiation of nitrogen-saturated aqueous solutions containing aluminum phthalocyanine tetrasulfonate (AlPcS4) at 675 nm in the presence of 2,5-dichloro-diaziridinyl-1,4-benzoquinone (AZDClQ) and hypoxanthine (HX) produces the oxidized HX

SUBSTITUTED XANTHINE DERIVATIVES

The present invention relates to compounds of formula (I) a process for their manufacture, pharmaceutical compositions containing them and their use in therapy, particularly in the treatment of conditions having an association with TRPC5 containing ion channels. R1, R2, R3, R4 and R5 have meanings given in the description.

Hydroxyl radical induced oxidation of theophylline in water: A kinetic and mechanistic study

Oxidative destruction and mineralization of emerging organic pollutants by hydroxyl radicals (OH) is a well established area of research. The possibility of generating hazardous by-products in the case of OH reaction demands extensive investigations on the degradation mechanism. A combination of pulse radiolysis and steady state photolysis (H2O2/UV photolysis) followed by high resolution mass spectrometric (HRMS) analysis have been employed to explicate the kinetic and mechanistic features of the destruction of theophylline, a model pharmaceutical compound and an identified pollutant, by OH in the present study. The oxidative destruction of this molecule, for intermediate product studies, was initially achieved by H2O 2/UV photolysis. The transient absorption spectrum corresponding to the reaction of OH with theophylline at pH 6, primarily caused by the generation of (T8-OH), was characterised by an absorption band at 330 nm (k2 = (8.22 ± 0.03) × 109 dm3 mol-1 s-1). A significantly different spectrum (λmax: 340 nm) was observed at highly alkaline pH (10.2) due to the deprotonation of this radical (pKa ～ 10.0). Specific one electron oxidants such as sulphate radical anions (SO4-) and azide radicals (N 3) produce the deprotonated form (T(-H)) of the radical cation (T+) of theophylline (pKa 3.1) with k2 values of (7.51 ± 0.04) × 109 dm3 mol-1 s-1 and (7.61 ± 0.02) × 109 dm3 mol-1 s-1 respectively. Conversely, oxide radicals (O -) react with theophylline via a hydrogen abstraction protocol with a rather slow k2 value of (1.95 ± 0.02) × 109 dm3 mol-1 s-1. The transient spectral studies were complemented by the end product profile acquired by HRMS analysis. Various transformation products of theophylline induced by OH were identified by this technique which include derivatives of uric acids (i, iv & v) and xanthines (ii, iii & vi). Further breakdown of the early formed product due to OH attack leads to ring opened compounds (ix-xiv). The kinetic and mechanistic data furnished in the present study serve as a basic frame work for the construction of OH induced water treatment systems as well as to understand the biological implications of compounds of this kind. the Partner Organisations 2014.

Discovery of a bacterial 5-methylcytosine deaminase

5-Methylcytosine is found in all domains of life, but the bacterial cytosine deaminase from Escherichia coli (CodA) will not accept 5-methylcytosine as a substrate. Since significant amounts of 5-methylcytosine are produced in both prokaryotes and eukaryotes, this compound must eventually be catabolized and the fragments recycled by enzymes that have yet to be identified. We therefore initiated a comprehensive phylogenetic screen for enzymes that may be capable of deaminating 5-methylcytosine to thymine. From a systematic analysis of sequence homologues of CodA from thousands of bacterial species, we identified putative cytosine deaminases where a "discriminating" residue in the active site, corresponding to Asp-314 in CodA from E. coli, was no longer conserved. Representative examples from Klebsiella pneumoniae (locus tag: Kpn00632), Rhodobacter sphaeroides (locus tag: Rsp0341), and Corynebacterium glutamicum (locus tag: NCgl0075) were demonstrated to efficiently deaminate 5-methylcytosine to thymine with values of kcat/Km of 1.4 × 105, 2.9 × 104, and 1.1 × 103 M-1 s-1, respectively. These three enzymes also catalyze the deamination of 5-fluorocytosine to 5-fluorouracil with values of kcat/Km of 1.2 × 105, 6.8 × 104, and 2.0 × 102 M-1 s-1, respectively. The three-dimensional structure of Kpn00632 was determined by X-ray diffraction methods with 5-methylcytosine (PDB id: 4R85), 5-fluorocytosine (PDB id: 4R88), and phosphonocytosine (PDB id: 4R7W) bound in the active site. When thymine auxotrophs of E. coli express these enzymes, they are capable of growth in media lacking thymine when supplemented with 5-methylcytosine. Expression of these enzymes in E. coli is toxic in the presence of 5-fluorocytosine, due to the efficient transformation to 5-fluorouracil.

HAIR TREATMENT PRODUCTS COMPRISING POLYMERS

The invention relates to hair treatment products, comprising at least one copolymer made of 0.1 to 50% (in relation to the total number of monomers in the copolymer) monomers of the formula (I), wherein the unknowns are defined as in claim 1, and A2) are monomers from the group of acrylic acid, methacrylic acid and the like, and—optionally non-ionic monomers from the group of acrylamide, vinyl alcohol, and the like, wherein the monomers A2 and A3 together represent 50 to 99.9% (in relation to the total number of monomers in the copolymer) of the copolymer, at least one silicon and at least one selected care product, wherein the products result in advantageous effects for skin and hair.

One-step synthesis of lumazine and xanthine: First co-crystal of lumazine and perchloric acid with a unique monohydrated hydronium ion (H 5O2+) mediated supramolecular assembly of the lumazine dimer

A perchloric acid mediated one-step synthesis of lumazine derivatives from pterins and xanthine from guanine is reported. However, 2-pivaloylamino derivatives of pterins underwent simple hydrolysis of the pivaloylamino group generating free pterin compounds, but the 2-oxo derivatives, that is, the lumazine compounds, were not obtained. A novel supramolecular assembly is constructed by the unique hydrogen bonding of H5O2 + bridging two hydrogen-bonded dimers of lumazine to form the co-crystal 21 with aqueous perchloric acid. In contrast, N2-pivaloyl- 6-bromo-5-deazapterin was simply hydrolysed to form the protonated deazapterin 22, which forms a unique six-membered cyclic hydrogen-bonded structure leading to the generation of a polymeric supramolecular assembly. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.