Isolation and Characterization of a Protease Inhibitor from the Marine Gastropod Tugali gigas

A protease inhibitor, named tugalistatin, was isolated from the muscle of the marine gastropod Tugali gigas. Tugalistatin inhibited the proteolytic activity of trypsin and α-chymotrypsin. It also suppressed the activity of kallikrein as well as elastase to some extent. On the other hand, it was inactive against metallo-proteases and cysteine proteases. These suggest that tugalistatin is a serine protease inhibitor. In SDS-polyacryamide gel electrophoresis it showed a single band corresponding to 22,000 under reduced conditions. The molecular weight of intact inhibitor was calculated to be 17,000 when checked by FPLC on a Superose 12 column. Amino acid analysis revealed tugalistatin contained a large amount of glutamic acid (14.0%), half-cystine (11.1%), and aspartic acid (9.7%) in the molecule.