Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.17.1.4 (xanthine dehydrogenase)
 1,236 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Studies by e.p.r. (electron-paramagnetic-resonance) spectroscopy and by stopped-flow spectrophotometry on turkey liver xanthine dehydrogenase revealed strong similarities to as well as important differences from the Veillonella alcalescens xanthine dehydrogenase and milk xanthine oxidase. The turkey enzyme is contaminated by up to three non-functional forms, giving molybdenum e.p.r. signals designated Resting I, Resting II and Slow. Slow and to a lesser extent Resting I signals are like those from the Veillonella enzyme, whereas Resting II is very like a resting signal described by K. V. Rajagopolan, P. Handler, G. Palmer & H. Beinert (1968) (J. Biol. Chem. 243, 3784-3796) for aldehyde oxidase. Another non-functional form that gives the Inhibited signal is produced on treatment of the enzyme with formaldehyde. Stopped-flow measurements at 450 nm show that, as for the milk enzyme, reduction by xanthine is rate-limiting in enzyme turnover. The active enzyme gives rise to Very Rapid and Rapid molybdenum(V) e.p.r. signals, as well as to an FADH signal. That these signals are almost indistinguishable from those of the milk enzyme, confirms the similarities between the active sites. There are two types of iron-sulphur centres that give signals like those in the milk enzyme, though with slightly different parameters. Quantitative reduction titration of the functional enzyme with xanthine revealed two important differences between the turkey and the milk enzymes. First, the turkey enzyme FADH/FADH2 system has a redox potential sufficiently low that xanthine is incapable of reducing the flavin completely. This finding presumably explains the very low oxidase activity. Secondly, whereas the Fe/S II chromophore in the milk enzyme has a relatively high redox potential, for the turkey enzyme the value of this potential is lower and similar to that of its Fe/S I chromophore.
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PMID:Studies by electron-paramagnetic-resonance spectroscopy and stopped-flow spectrophotometry on the mechanism of action of turkey liver xanthine dehydrogenase. 17 33

Pseudomonas putida, strain 40, originally isolated by enrichment on caffeine as the sole source of carbon and nitrogen, has been developed to grow on 0.5% caffeine. The organism will grow on any N-methyl derivative of xanthine containing one or more methyl groups at the 1, 3, or 7 positions. An investigation of the activities of resting cell suspensions and cell-free preparations together with the detection of metabolic intermediates suggest that caffeine is first metabolized by the action of an enzyme which is capable of hydrolytically removing all three methyl groups with the production of methanol and free xanthine. The methanol presumably is oxidized to the final product, CO2, through the sequential action of methanol, formaldehyde, and formate dehydrogenases, which are induced by growth on caffeine. Furthermore, the xanthine would seem to be channeled through conventional pathways of purine degradation through the action of xanthine dehydrogenase and uricase, both induced by growth on caffeine. However, a variety of data suggests that the metabolism of caffeine may be compartmentalized in the cell and metabolized separately from externally added xanthine. Additional studies indicated that the cell is permeable to the methylxanthines. The significance of these findings is discussed.
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PMID:Metabolism of N-methylpurines by a Pseudomonas putida strain isolated by enrichment on caffeine as the sole source of carbon and nitrogen. 115 47