A serine endopeptidase from the fruits of Melothria japonica (Thunb.) maxim.

An endopeptidase from the fruits of Melothria japonica (Thunb.) Maxim. has been purified by DEAE-Sepharose chromatography and gel-filtration by a Sephacryl S-300. The enzyme has Mr of 61 kDa. The optimum pH of the enzyme was 8. The enzyme activity was inhibited by diisopropyl fluorophosphate and phenylmethanesulfonylfluoride, but not by EDTA. Casein was a poor substrate, but angiotensin I was cleaved by the enzyme within 30 min at four different sites. These results indicated that the enzyme was a serine oligopeptidase of broad substrate specificity.