Homologies in serine proteinases

Abstract

Bovine pancreatic juice contains approximately equal amounts of four inactive precursors of endopeptidases (zymogens): chymotrypsinogen A, chymotrypsinogen B, trypsinogen (Keller, Cohen & Neurath 1958) and a component of procarboxypeptidase which resembles a chymotrypsinogen (Brown, Greenshields, Yamasaki & Neurath 1963). In porcine pancreas another endopeptidase, elastase, is found which is uniquely effective against elastin, the elastic protein of ligaments. Chymotrypsin A and chymotrypsin B are almost identical in enzyme activity (Enenkel & Smillie 1963), but the chymotrypsins, trypsin and elastase have widely different substrate specificities, as seen, for example, in their action on the B chain of oxidized insulin (Naughton & Sanger 1961; figure 1).