单词	xanthine
释义	xanthine /ˈzanθiːn / noun [mass noun] Biochemistry 1A crystalline compound found in blood and urine which is an intermediate in the metabolic breakdown of nucleic acids to uric acid. A purine derivative; chemical formula: C5H4N4O2. Xanthine oxidase catalyses the oxidation of xanthine and hypoxanthine to uric acid and is a well-known producer of superoxide radicals.... It appears that the purine metabolic system in humans has found a way to avoid the overproduction of uric acid by downregulating the Xor gene expression, the product converting hypoxanthine to xanthine and further xanthine to uric acid. Xanthine oxidase activity was evaluated by the spectrophotometric measurement of the formation of uric acid from xanthine. 1.1 [count noun] Any of the derivatives of this, including caffeine and related alkaloids.Methyl xanthines (caffeine, theophylline and theobromine) are found in seeds and leaves of a variety of unrelated plant species, including coffee, tea, cocoa, cola and mate.... Ephedrine and the xanthines, such as caffeine and theophylline, increase metabolic rate. The main components of this tea are natural xanthines such as caffeine, theobromine, theophylline and tanni. Origin Mid 19th century: from xanthic + -ine4.
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