Purification and Characterization of Extracellular Cysteine Protease Inhibitor from Chlorella sp.

Abstract

An extracellular cysteine protease inhibitor (ECPI) from Chlorella sp. was purified to homogeneity by DEAE-Cellulose column chromatography and Sephacryl S-300 column chromatography. The molecular mass of the inhibitor was estimated to be 284 kDa by SDS-PAGE and 285 kDa by gel filtration on Sephacryl S-300 column chromatography. ECPI retained 100 % of its original activity even after heating at 100°C for 20 min. It showed an inhibitory activity against the proteolytic activity of papain, ficin, chymopapain, calcium activated protease (calpain) and bromelain, but not against trypsin or α-chymotrypsin. ECPI contained 83.4% carbohydrate residues by weight and inhibited papain at a ratio of 1 : 1. The inactivated inhibitor, treated by sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (2-ME), was reactivated by keeping it at 10°C and pH 8.5 after elimination of SDS and 2-ME.