Über Proteaseinhibitoren, V1. Zur Chemie und Physiologie der spezifischen Trypsininhibitoren aus den Bauchspeicheldrüsen von Rind, Hund, Schwein und Mensch

Abstract

Each of the specific trypsin inhibitors, isolated from the pancreatic glands of pig, dog and ox is further resolved by electrophoresis into three inhibitory fractions. The amino acid composition is the same or only slightly different for each of the three fractions from one inhibitor. The molecular weights of the inhibitors from pancreatic glands, calculated from the amino acid composition, are dog, 5636 (53 amino acids); pig, 5695 (53 amino acids); ox, 5919 (54 amino acids); the content of amide groups has not been taken into account. Each of the inhibitors from the 3 species contains 2 tyrosine residues, but not tryptophan, histidine or phenylalanine. The three inhibitors described here, and the inhibitor from human pancreatic secretion do not inhibit [alpha]-chymotrypsin, kallikreins, plasmin, thrombin or papain. In each case, the equilibrium between trypsin and inhibitor is established very rapidly, and the inhibition then remains constant from pH 5.5 to 11. The inhibitors from human pancreatic secretion and from pig pancreas inhibit trypsin stoichiometrically up to 100%, while 50-60% excess of the inhibitors from the pancreas of dog and ox (on the basis of 1:1[long dash]inhibitor:trypsin) is required for complete inhibition. The inhibitor from ox pancreas behaves non-competitively; the 3 other inhibitors behave competitively towards trypsin in the presence of N-benzoyl-DL-arginine-p-nitroanilide. The 4 inhibitors show the phenomenon of temporary inhibition: if the inhibitor is present in excess of the trypsin, it is degraded only very slowly at pH 7.8 and 37 . On the other hand, free trypsin degrades the inhibitor when it is bound in the complex, relatively quickly, depending on the concentration of the complex and the degree of inhibition. Chymotrypsin also degrades the 4 inhibitors at 37 . In the case of the inhibitor from dog pancreas the mode of secretion and the distribution of the inhibitor in the tissue were studied. Since the concentration of inhibitor in the tissue and in the secretion shows a marked parallelism with the concentration of trypsinogen, it is concluded that the inhibitor is stored in the zymogen granules and is secreted together with the zymogens. Its importance may lie in the prevention of the premature activation of the trypsinogen in the gland or in the duct system.