The specificity of porcine pancreatic protease E

A procedure for the preparation of porcine protease E is described. The availability of a convenient source of the enzyme has permitted specificity studies utilizing the macromolecular substrates oxidized insulin A and B chains and oxidized ribonuclease. The results show that protease E has a pronounced selectivity for the carbonyl bonds of serine threonine, alanine, and valine residues, with the latter most favored. The specificity is complementary to that of the chymotrypsins and we suggest that this property is physiologically significant. The k3 and Km values for the substrates acetyl-trialanine methyl ester, succinyltrialanine p-nitroanilide and benzoylalanine methyl ester are comparable to those observed by others for porcine elastase. The specificity observed in the present work, however, indicates that protease E may best be regarded as a member of the chymotrypsin group of enzymes.