Proteolytic activity and cleavage specificity of cathepsin E at the physiological pH as examined towards the B chain of oxidized insulin

Abstract

Proteolytic activity and cleavage specificity of cathepsin E were investigated in a wide range of pHs from 3.0 to 10.5 using the B chain of oxidized insulin as substrate. Contrary to the previous notion that cathepsin E is virtually inactive above pH 6, significant proteolytic activity was observed at pH 7.4 and above. Further, cleavage specificity appeared to change significantly with pH and rather specific cleavage occurred at pH 7.4 and above as compared to pH 5.5 and 3.0. These results suggest that cathepsin E may function in vivo at the physiological pH with a rather restricted specificity.