| xanthine ribonucleoside | 9-beta-d-ribosylxanthine;the deamination product of guanosine (O replacing -NH2). Synonym: xanthine ribonucleoside. Abbreviation: Xao (05 Mar 2000) |
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| ribonucleoside | <biochemistry> A nucleoside in which purine or pyrimidine base is linked to a ribose molecule. (09 Oct 1997) |
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| ribonucleoside diphosphate reductase | <enzyme> An enzyme of the oxidoreductase class that catalyses the formation of 2'-deoxyribonucleotides from the corresponding ribonucleotides using NADPH as the ultimate electron donor. The deoxyribonucleoside diphosphates are used in DNA synthesis. Chemical name: 2'-Deoxyribonucleoside-diphosphate:oxidised-thioredoxin 2'-oxidoreductase Registry number: EC 1.17.4.1 (12 Dec 1998) |
| ribonucleoside-triphosphate reductase | <enzyme> Requires a cobamide coenzyme and ATP Registry number: EC 1.17.4.2 Synonym: rtp reductase (26 Jun 1999) |
| cytosine ribonucleoside | <biochemistry> Nucleoside consisting of D ribose and the pyrimidine base cytosine. (18 Nov 1997) |
| purine ribonucleoside | A toxic nucleoside isolated from the mushroom Agaricus nebularis and from Streptomyces sp. Synonym: 9-beta-ribofuranosylpurine, purine ribonucleoside, ribosylpurine. (05 Mar 2000) |
| methyl xanthine | <chemical, drug> Naturally occurring purine alkaloids such as theobromine, theophylline and caffeine (trimethyl xanthine). They inhibit cAMP phosphodiesterase and thus cause an increase in the intracellular cAMP concentration. (18 Nov 1997) |
| xanthine | <biochemistry> A purine, the starting point for purine degradation. Its methylated derivatives (theophylline, theobromine, caffeine) are potent cAMP phosphodiesterase inhibitors. (18 Nov 1997) |
| xanthine alkaloids | Alkaloids, which contain xanthine as their nitrogenous base. (12 Dec 1998) |
| xanthine bronchodilator | <pharmacology> A group of medications that work by a common mechanism to effect bronchodilation (open up air passages) in the lungs. Used in the treatment of asthma and related conditions. Examples include: theophylline, aminophylline and dyphylline. (27 Sep 1997) |
| xanthine dehydrogenase | <enzyme> An enzyme that catalyses the oxidation of xanthine in the presence of NAD+ to form urate and NADH. It acts also on a variety of other purines and aldehydes. Chemical name: Xanthine:NAD+ oxidoreductase Registry number: EC 1.1.1.204 (12 Dec 1998) |
| xanthine nucleotide | The monophosphoric ester of xanthosine. An intermediate in GMP biosynthesis. Synonym: xanthidylic acid, xanthine nucleotide, xanthylic acid. (05 Mar 2000) |
| xanthine oxidase | <enzyme> Dehydrogenases involved in conversion of hypoxanthine to xanthine and xanthine to uric acid, as the final catabolism of purines. Deficient in the human disease xanthinuria. (18 Nov 1997) |
| hypoxanthine-guanine-xanthine phosphoribosyltransferase | <enzyme> From tritrichomonas foetus; in contrast to EC 2.4.2.8, this enzyme also uses xanthine as substrate; mw 24 kD Registry number: EC 2.4.2.- Synonym: hgxprtase (26 Jun 1999) |
| desulfo xanthine dehydrogenase | <enzyme> Naturally occuring inactive form of xanthine dehydrogenase Registry number: EC 1.1.1.- (26 Jun 1999) |