- α-Amino-β-(4-imidazolyl)propionic acid; the l-isomer is a basic amino acid found in most proteins. It is a nutritionally essential amino acid in mammals.- h. ammonia-lyase an enzyme catalyzing deamination of l-h. to urocanate and ammonia; this enzyme is absent or deficient in individuals with histidinemia. SYN: histidase, histidinase, h. deaminase.- h. decarboxylase an enzyme catalyzing the pyridoxal-phosphate-dependent decarboxylation of l-h. to histamine and CO2; thus, it plays a role in constriction of bronchial smooth muscle.
* * *his·ti·dine 'his-tə-.dēn n a crystalline essential amino acid C6H9N3O2 formed by the hydrolysis of most proteins abbr. His
* * *n.
* * *his·ti·dine (hisґtĭ-dēn) an essential amino acid, α-amino-1H-imidazole-4-propanoic acid, first found as a decomposition product of the protamine of sturgeon testes; it is obtainable from many proteins by the action of sulfuric acid and water. The decarboxylation of histidine results in the formation of histamine. Symbols His and H. See table at amino acid.
Medical dictionary. 2011.