[Action of two thiol proteinases from the spleen which are active in neutral media on vasoactive peptides].

The action of two earlier isolated highly purified spleen thiol proteinases on angiotensins I and II, bradykinin and kallidin was investigated. It was demonstrated that proteinase I which is apparently cathepsin L from bovine spleen brings about rapid inactivation of angiotensin II with a splitting of the Tyr-Ile bond and a formation of two tetrapeptides. Proteinases I also split angiotensin I. Proteinase I partially inactivates bradykinin and kallidin by splitting the Gly4-Phe5 bond. The activity of proteinase I toward angiotensin II is about 50 times higher than that toward bradykinin. The corresponding values of Km and V are 7.5 X 10(-5) M and 10.0 mumole/min/mg. The possible role of proteinase I in angiotensin II inactivation under physiological conditions is discussed. Proteinase II converts kallidin to bradykinin by splitting off the N-terminal lysine. Proteinase II causes partial inactivation of bradykinin by splitting of the Gly4-Phe5 and Phe5-Ser6 bonds of this peptide. Proteinase II possesses both aminopeptidase and endopeptidase activities and is therefore cathepsin H from spleen. Proteinase II does not split either angiotensin I or angiotensin II.