Histaminase

HISTAMINASE is the name which has been applied [Best and McHenry, 1930] to a histamine-inactivating enzyme. Originally found by Best [1929] to be present in ox and horse lung, investigations on the histaminase content of dog tissues showed it to be most plentifully contained in the kidney and in the intestinal mucosa. These studies, utilising fresh tissue in vitro, led to perfusion experiments in which it was found that isolated dog kidneys could inactivate large amounts of histamine. The obvious suggestion has been made that this enzymic mechanism, functioning principally in the kidney and in the wall of the small intestine, may constitute one of the body's protections against harm- ful amounts of histamine. Some of the properties of histaminase have been previously described. It is heat-labile, being irreversibly inactivated at 600. For its activity the optimal temperature is 380, and the optimal PH range is from 6-9 to 8-0. The enzyme is inhibited slightly by ammonium and magnesium ions, and markedly by calcium, while it is not affected by sodium and potassium. Of the anions, chloride is without effect, sulphate and citrate are inhibitory, and phosphate definitely augments the reaction. As it was found that the histamine-hista- minase reaction does not occur in presence of M/2000 potassium cyanide, proceeds very slowly in an atmosphere of nitrogen, and is accelerated by oxygen, it has been thought to be oxidative. Under certain conditions, if not always, the enzyme causes disruption of the iminazole ring in the histamine molecule.