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

Abstract

An intracellular cysteine protease inhibitor (ICPI) from Chlorella sp. was purified to homogeneity judging from polyacrylamide gel electrophoresis. The purified inhibitor had a molecular mass of 410kDa and a pI of 5.3. ICPI retained 100% of the original activity even after heating at 100°C for 5 min. It exhibited an inhibitory activity against the proteolytic activity of papain, ficin, chymopapain, calcium dependent neutral protease and bromelain, but not against cathepsin B, pepsin, trypsin, or α-chymotrypsin. The inhibitory activity was inactivated by α-chymotrypsin. ICPI contained 76% carbohydrate residues by weight and inhibited papain at a ratio of 1:3. From these results, we assume that ICPI is a novel type of cysteine protease inhibitor.