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.
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