2,5-Diaminovaleric acid; the l-isomer is the amino acid formed when l-arginine is hydrolyzed by arginase; not a constituent of proteins, but an important intermediate in the urea cycle; elevated levels seen in certain defects of the urea cycle.
- o. δ-aminotransferase an enzyme that will reversibly catalyze the reaction of α-ketoglutarate and l-o. to form l-glutamate and l-glutamate γ-semialdehyde; a deficiency of this enzyme will result in gyrate atrophy of the choroid and retina. SYN: o. transaminase.
- o. carbamoyltransferase an enzyme catalyzing formation of l-citrulline and orthophosphate from l-o. and carbamoyl phosphate; a part of the urea cycle; a deficiency of this enzyme will result in ammonia intoxication and impaired urea formation. SYN: o. transcarbamoylase.
- o. decarboxylase an enzyme catalyzing the decarboxylation of l-o. to putrescine and CO2; first step in polyamine biosynthesis.
- o. transaminase SYN: o. δ-aminotransferase.
- o. transcarbamoylase SYN: o. carbamoyltransferase.
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or·ni·thine 'ȯr-nə-.thēn n a crystalline amino acid C5H12N2O2 that functions esp. in urea production as a carrier by undergoing conversion to citrulline and then arginine in reaction with ammonia and carbon dioxide followed by recovery along with urea by enzymatic hydrolysis of arginine
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n.
an amino acid produced in the liver as a by-product during the conversion of ammonia to urea.
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or·ni·thine (orґnĭ-thēn) an amino acid produced in the urea cycle by the splitting off of urea from arginine and is itself converted into citrulline. On decomposition, it gives rise to putrescine.Medical dictionary. 2011.