Xanthine

A substance found in caffeine, theobromine, and theophylline and encountered in tea, coffee, and the colas. Chemically, xanthine is a purine. There is a genetic disease of xanthine metabolism, xanthinuria, due to deficiency of an enzyme, xanthine dehydrogenase, needed to process xanthine in the body. Unchecked, xanthinuria can lead to kidney stone formation and urinary tract disease (due to xanthine stones) and to muscle disease (due to deposits of xanthine in the muscle). Treatment is by avoiding foods and drinks containing xanthine derivatives, such as coffee, tea, and colas. The name "xanthine" was taken from the Greek "xanqos" meaning yellow + quinine since it forms yellow salts and its solution forms a blue fluorescence as does quinine.

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2,6-Dioxopurine; 2,6-(1H,3H)-purinedione; oxidation product of guanine and hypoxanthine, precursor of uric acid; occurs in many organs and in the urine, occasionally forming urinary calculi; elevated in molybdenum cofactor deficiency and in xanthinuria.

- x. dehydrogenase an oxidoreductase oxidizing x. to urate with NAD⁺ as the oxidant; lower activity in individuals with a deficiency of molybdenum cofactor.

- x. nucleotide SYN: xanthosine 5′-monophosphate.

- x. oxidase a flavoprotein containing molybdenum; an oxidoreductase catalyzing the reaction of x., O₂, and H₂O to produce urate and superoxide; also oxidizes hypoxanthine, some other purines and pterins, and aldehydes. A lower activity is observed in molybdenum cofactor deficiency. SYN: hypoxanthine oxidase, Schardinger enzyme.

- x. ribonucleoside SYN: xanthosine.

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xan·thine 'zan-.thēn n a feebly basic compound C₅H₄N₄O₂ that occurs esp. in animal or plant tissue, is derived from guanine and hypoxanthine, and yields uric acid on oxidation also any of various derivatives of this

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n.

a nitrogenous breakdown product of the purines adenosine and guanine. Xanthine is an intermediate product of the breakdown of nucleic acids to uric acid.

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xan·thine (X) (zanґthēn) [Gr. xanthos yellow, from the yellow color of its nitrate] a purine base found in most body tissues and fluids, certain plants, and some urinary calculi. It is an intermediate in the degradation of adenosine monophosphate to uric acid, being formed by oxidation of hypoxanthine. Methylated xanthines (see methylxanthine) are used medicinally. Xanthine also occurs complexed with ribose as xanthose.