Topic
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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TL;DR: A method is described by which plasma or serum concentrations of uric acid and hypoxanthine/xanthine may be determined in a two-step sequential method based on the principle that hydrogen peroxide is coupled to the production of a coloured product.
38 citations
TL;DR: The results indicated that this kinetic uricase method using this uric enzyme was reliable for serum uric acid assay with enhanced resistance to xanthine besides other common errors.
Abstract: An intracellular uricase from Bacillus fastidious A.T.C.C. 26904 was characterized and evaluated for serum uric acid assay by a patented kinetic uricase method. The active uricase was 151 kDa by gel filtration through Sephadex G-200. Both SDS/PAGE and matrix-assisted laser-desorption ionization-time-of-flight MS resolved a single polypeptide with a molecular mass of approx. 36.0 kDa. The N-terminal sequence was AERTMFYGKGDV. The optimum pH for this uricase ranged from 9.0 to 10.5. At pH 9.2, the Km (Michaelis-Menten constant) was 204+/-14 micromol/l (n=8) and the Ki (inhibition constant) for xanthine was 41+/-7 micromol/l (n=5). By analysing the data monitored within 5 min at 0.03 unit/ml uricase, this kinetic uricase method gave linear response to uric acid in reaction solution from 1.3 to 60 micromol/l. Aside from other common errors, 30 micromol/l xanthine in the reaction solution caused no error in this kinetic uricase method, while it caused negative error in the indirect equilibrium method by peroxidase-coupled assay of H2O2. Uric acid in clinical sera by this kinetic uricase method (Ck) closely and positively correlated with that from the indirect equilibrium method (Ce) (Ck = 0.008+1.081 x Ce, r>0.990, n=99). However, Bland-Altman analysis suggested inconsistency between Ck and Ce. These results indicated that this kinetic uricase method using this uricase was reliable for serum uric acid assay with enhanced resistance to xanthine besides other common errors.
38 citations
TL;DR: It is concluded that caffeine, which is known to have antioxidant properties, impedes keratinocyte proliferation and migration, suggesting that it may have an inhibitory effect on wound healing and epithelialisation.
Abstract: The purine alkaloid caffeine is a major component of many beverages such as coffee and tea. Caffeine and its metabolites theobromine and xanthine have been shown to have antioxidant properties. Caffeine can also act as adenosine-receptor antagonist. Although it has been shown that adenosine and antioxidants promote wound healing, the effect of caffeine on wound healing is currently unknown. To investigate the effects of caffeine on processes involved in epithelialisation, we used primary human keratinocytes, HaCaT cell line and ex vivo model of human skin. First, we tested the effects of caffeine on cell proliferation, differentiation, adhesion and migration, processes essential for normal wound epithelialisation and closure. We used 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) proliferation assay to test the effects of seven different caffeine doses ranging from 0·1 to 5 mM. We found that caffeine restricted cell proliferation of keratinocytes in a dose-dependent manner. Furthermore, scratch wound assays performed on keratinocyte monolayers indicated dose-dependent delays in cell migration. Interestingly, adhesion and differentiation remained unaffected in monolayer cultures treated with various doses of caffeine. Using a human ex vivo wound healing model, we tested topical application of caffeine and found that it impedes epithelialisation, confirming in vitro data. We conclude that caffeine, which is known to have antioxidant properties, impedes keratinocyte proliferation and migration, suggesting that it may have an inhibitory effect on wound healing and epithelialisation. Therefore, our findings are more in support of a role for caffeine as adenosine-receptor antagonist that would negate the effect of adenosine in promoting wound healing.
38 citations
TL;DR: The results support the contention that the distantly related transporters of COG2233 and COG2252 use topologically similar side chain determinants to dictate their function and the distinct purine selectivity profiles.
38 citations
TL;DR: In this article, a model of the interaction of substrates and inhibitors with xanthine oxidase (XO) based on similarity concepts and molecular modeling is introduced and discussed, and previous literature is reexamined in the light of recent insights into the mechanism and structure of XO.
Abstract: A model of the interaction of substrates and inhibitors with xanthine oxidase (XO) based on similarity concepts and molecular modeling is introduced and discussed, and previous literature is reexamined in the light of recent insights into the mechanism and structure of XO. Use is made of quantum-chemical calculations with the inclusion of solvent effects, molecular superimposition with least-squares fitting algorithms, and molecular electrostatic potentials. First, the relative stabilities of the tautomeric forms of the physiological substrates, xanthine and hypoxanthine, are calculated both in vacuo and in water in order to select the most abundant form(s) at physiological pH: the two substrates prove to be stable in their lactam forms, with a dominance of the N7-H tautomer for xanthine and of N9-H for hypoxanthine. The structures of xanthine and hypoxanthine are then superimposed, and their relative orientation with respect to the molybdenum center of XO is suggested. The criteria used for superimposit...
38 citations