Histidine

histidine

[′his·tə‚dēn]

(biochemistry)

C₆H₉O₂N₃ A crystalline basic amino acid present in large amounts in hemoglobin and resulting from the hydrolysis of most proteins.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Histidine

 

(α-amino-β-imidazole-propionic acid):

an amino acid with basic characteristics, essential in many animals; the human body is capable of limited synthesis of histidine. It is one of the ingredients of the active centers of many enzymes, in particular of ribonuclease and transketolase. The initial stage of the enzymatic destruction of histidine in the body is the splitting off of ammonia, with the formation of urocanic acid, which is discharged in the urine. The deamination of histidine is an irreversible reaction and is catalyzed by the enzyme histidine ammonia lyase (histidine-a-deaminase), which is found in the liver of animals and in bacteria. Histidine deficiency leads to many metabolic disturbances, including inhibition of hemoglobin synthesis. Histidine is a precursor of the specific dipeptides of the skeletal musculature—carnosine and anserine. Decarboxylation of histidine leads to the formation of the biologically active amine histamine; this process is catalyzed by histidine decarboxylase, an enzyme belonging to the class of lyases. This enzyme acts only on the L-isomer (natural form) of histidine. The reaction is reversibly inhibited by the respiratory inhibitors cyanide, hydroxylamine, and semicarbazide.

A. A. BOLDYREV and E. V. PETUSHKOVA

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.