- 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.
* * *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
* * *n.
* * *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.