Histamine is produced by
a. Decarboxylation of histidine — forms histamine reaction is catabolized by Aromatic —L — amino acid. Decarboxylase (that also catalyze decarboxylation of Dopa, 5-Hydroxytryptophan, phenylalanine, tyrosine and tryptophan).
b. Histidine compounds present in the human body include Ergothioneine, carnosine, and dietary anserine.
c. 3-Methyihistidine, present in normal human urine at a conc. of about 50 mg/dL, is unusually low in the urine of patients with Wilson’s disease.