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Xanthine

About: Xanthine is a research topic. Over the lifetime, 4046 publications have been published within this topic receiving 129820 citations. The topic is also known as: Xanthine.


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Journal ArticleDOI
TL;DR: Results indicate that uric acid is an effective inhibitor of the formation of superoxide and hydrogen peroxide by xanthine oxidase at the levels found in human plasma, suggesting that plasma uric Acid may play an important role in attenuating the oxidant-mcdiated tissue damage caused byxanthine oxidation released into the circulation during ischemia-reperfusion.
Abstract: D.:I.P.], ntrtl Dio.siuii.~iic.~ atrd ljiot~~(ri/~e~t~ ~(riic.~ ]K.:I.K.], Lrtrive~r.siij~ ~~/':I/(I~J~I~I( I (11 I~irt~ritr,q/ru~ ~~, llirt~~it~,q/~ut ~~, ..I/(I~I(I~~I(I 35233, utrd D~parit~lc~rli of Biochrn~~i.sirj~/R. R.], Fucrtlrj~ c!f,\lc~c/icit~c~. //rep Utri~~c,r.sirj. (!///rep Rcprrt~lic. .\lotr/cvidc~o. Urrr,yrruj. ABSTRAn. Xanthine osidase, a key source of reactive oxygen species, and purine substrates are detected in the circulation after ischemia-reperfusion. Iiigh levels of uric acid, produced by a santhine osidase-catalyzed reaction, are found in human plasma. \\'e studied whether uric acid could alter xanthine osidase activity in plasma obtained from eight adults and eight neonates. Known amounts of uric acid were added to santhine and santhine osidasesupplemented buffer and plasma, and the production of uric acid and superoside was determined. Uric acid, 150 and 300 phi, decreased the oxidation of santhine to uric acid in adult plasma by 37.5 f 5.6 and 48.9 f 6.1% and formation of superoside by 23.2 f 1.9 and 32.0 f 2.3%, respectively, compared with plasma without uric acid. In newborn plasma, a similar pattern and estent of inhibition was observed. Superoside formation, however, was inhibited to a greater estent than in adult plasma. Endogenous xanthine osidase was detected in newborn plasma in nine additional neonates using IIPLC. These results indicate that uric acid is an effective inhibitor of the formation of superoside and hydrogen peroxide by santhine osidase at the levels found in human plasma. Plasma uric acid may play an important role in attenuating the oxidant-mediated tissue damage caused by santhine osidase released into the circulation during ischemia-reperfusion.

81 citations

Journal ArticleDOI
TL;DR: This work reports the first report of bacterial N-demethylase genes that enable bacteria to live on caffeine and represent a new class of Rieske oxygenases and have the potential to produce biofuels, animal feed, and pharmaceuticals from coffee and tea waste.
Abstract: The molecular basis for the ability of bacteria to live on caffeine as a sole carbon and nitrogen source is unknown. Pseudomonas putida CBB5, which grows on several purine alkaloids, metabolizes caffeine and related methylxanthines via sequential N-demethylation to xanthine. Metabolism of caffeine by CBB5 was previously attributed to one broad-specificity methylxanthine N-demethylase composed of two subunits, NdmA and NdmB. Here, we report that NdmA and NdmB are actually two independent Rieske nonheme iron monooxygenases with N(1)- and N(3)-specific N-demethylation activity, respectively. Activity for both enzymes is dependent on electron transfer from NADH via a redox-center-dense Rieske reductase, NdmD. NdmD itself is a novel protein with one Rieske [2Fe-2S] cluster, one plant-type [2Fe-2S] cluster, and one flavin mononucleotide (FMN) per enzyme. All ndm genes are located in a 13.2-kb genomic DNA fragment which also contained a formaldehyde dehydrogenase. ndmA, ndmB, and ndmD were cloned as His(6) fusion genes, expressed in Escherichia coli, and purified using a Ni-NTA column. NdmA-His(6) plus His(6)-NdmD catalyzed N(1)-demethylation of caffeine, theophylline, paraxanthine, and 1-methylxanthine to theobromine, 3-methylxanthine, 7-methylxanthine, and xanthine, respectively. NdmB-His(6) plus His(6)-NdmD catalyzed N(3)-demethylation of theobromine, 3-methylxanthine, caffeine, and theophylline to 7-methylxanthine, xanthine, paraxanthine, and 1-methylxanthine, respectively. One formaldehyde was produced from each methyl group removed. Activity of an N(7)-specific N-demethylase, NdmC, has been confirmed biochemically. This is the first report of bacterial N-demethylase genes that enable bacteria to live on caffeine. These genes represent a new class of Rieske oxygenases and have the potential to produce biofuels, animal feed, and pharmaceuticals from coffee and tea waste.

81 citations

Journal ArticleDOI
TL;DR: Using calcium carbonate nanoparticles as enzyme immobilization matrix, the developments of xanthine biosensor were achieved by both electrooxidation and electroreduction of the enzymatic-generated hydrogen peroxide based on XnOx and horseradish peroxidase (HRP).
Abstract: Using calcium carbonate nanoparticles as enzyme immobilization matrix, the developments of xanthine biosensor were achieved by both electrooxidation and electroreduction of the enzymatic-generated hydrogen peroxide based on xanthine oxidase (XnOx) and horseradish peroxidase (HRP). Amperometric detection of xanthine was evaluated by holding the modified electrode at 0.55 and −0.05 V (versus SCE), for XnOx/Nano-CaCO 3 and XnOx/HRP/Nano-CaCO 3 , respectively. The linear dynamic ranges of anodic and cathodic detections of xanthine were between 2 × 10 −6 to 2.5 × 10 −4 M and 4 × 10 −7 to 5 × 10 −5 M, respectively. The detection limits were determined to be of 2 × 10 −6 and 1 × 10 −7 M with anodic and cathodic processes, respectively. At lower working potential, XnOx/HRP/Nano-CaCO 3 /GCE bienzymatic system exhibited excellent selectivity; the bienzyme electrode was inert towards ascorbic and uric acid present. Moreover, the permeability of enzyme/Nano-CaCO 3 was evaluated by the use of rotating disk electrode voltammetry.

81 citations

Journal ArticleDOI
A. Kooij1
TL;DR: The present review summarizes information that has become available about Xanthine oxidoreductase and Interpretations of contradictory findings are presented in order to reduce confusion that still exists with respect to the role of this enzyme in physiology and pathology.
Abstract: Xanthine oxidoreductase is an enzyme which has the unusual property that it can exist in a dehydrogenase form which uses NAD+ and an oxidase form which uses oxygen as electron acceptor. Both forms have a high affinity for hypoxanthine and xanthine as substrates. In addition, conversion of one form to the other may occur under different conditions. The exact function of the enzyme is still unknown but it seems to play a role in purine catabolism, detoxification of xenobiotics and antioxidant capacity by producing urate. The oxidase form produces reactive oxygen species and, therefore, the enzyme is thought to be involved in various pathological processes such as tissue injury due to ischaemia followed by reperfusion, but its role is still a matter of debate. The present review summarizes information that has become available about the enzyme. Interpretations of contradictory findings are presented in order to reduce confusion that still exists with respect to the role of this enzyme in physiology and pathology.

80 citations

Journal ArticleDOI
TL;DR: The results suggest that the use of Erythrina stricta for the treatment of gout could be attributed to its xanthine oxidase inhibitory activity.

80 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202361
2022108
202157
202060
201961
201869