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(organic chemistry)
C5H4N4O2 A toxic yellow-white purine base that is found in blood and urine, and occasionally in plants; it is a powder, insoluble in water and acids, soluble in caustic soda; sublimes when heated; used in medicine and as a chemical intermediate. Also known as dioxopurine.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(2,6-dioxopurine) an intermediate product of the metabolic degradation of purine bases. Its structural formula is

Xanthine forms yellow crystals. Its melting point is 220°C (with decomposition), and its molecular weight is 152.12. Xanthine dissolves poorly in water and better in alcohol. It displays the properties of a weak acid and a weak base. Widely found in nature (in small amounts), it is formed during the hydrolytic deamination of guanine or as a result of the aerobic oxidation of hypoxanthine in the presence of the enzyme xanthine oxidase. This enzyme also oxidizes xanthine to the final product of purine metabolism in man—uric acid—and this serves as a basis for xanthine determination. When this stage of xanthine metabolism is disrupted, xanthine accumulates in the body, primarily in the form of calcium salts (urinary calculus).

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Use of Methylxanthine Therapies for the Treatment and Prevention of Apnea of Prematurity.
At present, such a mechanism is thought to be the most important for interpreting the change in pharmacokinetic parameters of aromatic antibiotics on the consumption of food; a typical example is the direct interaction of the drug and of methylxanthines, which enter the organism in great amounts in food [37, 98, 99].
A later study by Saldana, et al, (21) looked at the extraction of methylxanthines from guarana seeds, mate leaves, and cocoa beans using supercritical carbon dioxide and ethanol.
Fact: In the early 1980s, women with fibrocystic breast disease - a condition characterized by painful but noncancerous breast lumps - were told they could control or cure it by removing from their diets all methylxanthines, a group of compounds that includes caffeine.
agonists ([beta.sub.2] agonists) and methylxanthines (theophylline).
Previous papers have reported that artificial parthenogenesis in sea stars can be induced--for example, by treatment with thymol or methylxanthine (Obata and Nemoto, 1984; Washitani-Nemoto et al., 1994).
The methylxanthine theophylline is effective in COPD, but is used less often than inhaled bronchodilators because of the potential for toxicity, given its narrow therapeutic index.
Researchers from the National Heart and Lung Institute of the Imperial College, London, examined the effects of theobromine, a methylxanthine derivative of cocoa, on cough.
Adding inhaled methylxanthine to initial bronchodilator therapy offered a small benefit in just one of three studies.
(i) Osteogenic medium (i) Explant method (1) ADMEM (ii) Part of UC: (2) 0.1 mM dexamethasone maternal, middle (3) 50 mM ascorbic acid and fetal (4) 10 mM glycerol-2-phosphate (ii) Adipogenic medium: (1) ADMEM (2) 500 mM isobutyl methylxanthine (3) 1 mM dexamethasone (4) Insulin (5) 100 mM indomethacin (6) 10 mM insulin (iii) Chondrogenic medium using comer (1) StemPro1Osteocyte/ Chondrocyte Di?erentiation Basal Medium; StemPro1 Chondrogenesis supplement; Gibco).
Pentoxifylline (PTX) is a methylxanthine derivative with chemical name of 1-5-oxohexyl-3,7-dimethylxanthine [21].