Hypodermin B, a Trypsin‐Related Enzyme from the Insect Hypoderma lineatum

Abstract

Hypodermin B, a serine proteinase with a molecular weight of 23000, was purified to homogeneity from the larvae Hypoderma lineatum. It is stoichiometrically inhibited by diisopropylfluorophosphate and fully inactivated by N‐tosyllysine chloromethyl ketone and soya bean and bovine pancreatic trypsin inhibitors. N‐Tosylphenyalanine chloromethyl ketone and ovomucoid are without effect on its activity. Hypodermin B hydrolyses both amide and ester substrates of trypsin but does not display any chymotryptic activity on synthetic substrates. Its specificity on the B chain of insulin is slightly broader than that of bovine trypsin. Its amino acid composition and N‐terminal sequence suggest structural homology with serine proteinases of the trypsin family and with two other serine proteinases, hypodermin A and Hypoderma collagenase, previously isolated from the same larave. Hypodermins A and B are very similar with respect to their inhibition and specificity, they differ however strongly from Hypoderma collagenase.