SPECIFIC HISTIDINE DECARBOXYLASES IN GASTRIC MUCOSA OF MAN AND OTHER MAMMALS - DETERMINATION, LOCATION AND PROPERTIES

Relatively high activities of the specific histidine decarboxylases were found in the gastric mucosa of men, monkeys, pigs, cows, dogs, cats, guinea-pigs, rabbits and rats. Some improvements of the assay of specific histidine decarboxylase were necessary, before these enzymes could be demonstrated in all stomachs investigated. The specific histidine decarboxylase could also be shown in the human gastric carcinomas. By pH-optima, substrate optima, Km, inhibition by α-methylhistidine but not by α-methyldopa, inhibition by benzene and activation by pyridoxal-5′-phosphate the histidine decarboxylases in the gastric mucosa could be characterized as specific histidine decarboxylases. The enzyme in the stomach of guinea-pigs has been purified 22-fold by ultracentrifugation and gelfiltration on Sephadex G 100. The demonstration of the specific histidine decarboxylases (isoenzymes) in the gastric mucosa of numerous mammals has some importance for the hypothesis of a physiological function of histamine as a chemostimulator of gastric secretion. Problems of the nomenclature of histidine decarboxylases are discussed. The terms acid" and "alkaline" histidine decarboxylases are proposed. © 1969."