Cysteine protease inhibitor in egg of chum salmon.

Two different cysteine protease inhibitors (Forms I and II) were isolated from chum salmon egg, and their molecular weights were found to be 16,000 and 11,000, respectively. When the N-terminal amino acid sequences of Forms I and II were compared, 67% of the residues were identical but no apparent homology was found between these inhibitors and cystatins of higher vertebrates. Because the amounts of half-cystine were estimated to be 7-8 residues per molecule, they can be classified into a new group of the cystatin superfamily.