The Separate Determination of Human Pepsin and Gastricsin.

The synthetic substrate, N-acetyl-L-phenylalanyl-L-diiodotyrosine was found to be hydrolyzed by pepsin but not at all by gastricsin. This difference has made possible the separate determination of pepsin and gastricsin in a mixture. The proteolytic activity of the mixture against APDT yielded the amount of pepsin present. The proteolytic activity of the mixture against bovine hemoglobin yielded the total amount of pepsin and gastricsin present. The amount of gastricsin was then simply calculated from the differences in these activities. The accuracy of the method was demonstrated using a reconstituted mixture of human pepsin and gastricsin. The content of pepsin and gastricsin in the native gastric juice was measured in 9 individuals both before and after histamine stimulation. Histamine stimulated the secretion of both pepsin and gastricsin.