| xanthidium | <botany> A genus of minute unicellular algae of the desmids. These algae have a rounded shape and are armed with glochidiate or branched aculei. Several species occur in ditches, and others are found fossil in flint or hornstone. Origin: NL, fr. Gr. Xanqos = yellow. Source: Websters Dictionary (01 Mar 1998) |
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| xanthidylic acid | The monophosphoric ester of xanthosine. An intermediate in GMP biosynthesis. Synonym: xanthidylic acid, xanthine nucleotide, xanthylic acid. (05 Mar 2000) |
| xanthin | 1. <physiology> A crystalline nitrogenous body closely related to both uric acid and hypoxanthin, present in muscle tissue, and occasionally found in the urine and in some urinary calculi. It is also present in guano. So called from the yellow colour of certain of its salts (nitrates). 2. <chemistry> A yellow insoluble colouring matter extracted from yellow flowers; specifically, the colouring matter of madder. [Formerly written also xanthein. 3. <chemistry> One of the gaseous or volatile decomposition products of the xanthates, and probably identical with carbon disulphide. Origin: Gr. Xanqos = yellow. Source: Websters Dictionary (01 Mar 1998) |
| 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) |
| xanthine ribonucleoside | 9-beta-d-ribosylxanthine;the deamination product of guanosine (O replacing -NH2). Synonym: xanthine ribonucleoside. Abbreviation: Xao (05 Mar 2000) |
| xanthinine | <chemistry> A complex nitrogenous substance related to urea and uric acid, produced as a white powder; so called because it forms yellow salts, and because its solution forms a blue fluorescence like quinine. Origin: Gr. Xanqos = yellow + quinine. Source: Websters Dictionary (01 Mar 1998) |
| xanthinol niacinate | <chemical> 3-pyridinecarboxylic acid compound with 3,7-dihydro-7- (2-hydroxy-3-((2-hydroxyethyl)methylamino)propyl)-1,3- dimethyl-1h-purine-2,6-dione (1:). A vasodilator used in peripheral vascular disorders and insufficiency. It may cause gastric discomfort and hypotension. Pharmacological action: vasodilator agents. Chemical name: 3-Pyridinecarboxylic acid, compd. With 3,7-dihydro-7-(2-hydroxy-3-((2-hydroxyethyl)methylamino)propyl)-1,3-dimethyl-1H-purine-2,6-dione (1:1) (12 Dec 1998) |
| xanthinuria | 1. Excretion of abnormally large amounts of xanthine in the urine. 2. A disorder resulting from defective synthesis of xanthine oxidase, characterised by urinary excretion of xanthine in place of uric acid, hypouricaemia, and, in some cases, the formation of xanthine stones; autosomal recessive inheritance. Synonym: xanthiuria, xanthuria. Origin: xanthine + G. Ouron, urine (05 Mar 2000) |
| xanthism | A pigmentary anomaly of blacks, characterised by red or yellow-red hair colour, copper-red skin, and often by dilution of iris pigment. Synonym: rufous albinism. Origin: G. Xanthos, yellowish (05 Mar 2000) |
| xanthium | <botany> A genus of composite plants in which the scales of the involucre are united so as to form a kind of bur; cocklebur; clotbur. Origin: NL, fr. Gr. Xanqion a plant used for dyeing the hair yellow, said to be the Xanthium strumarium, from xanqos = yellow. Source: Websters Dictionary (01 Mar 1998) |