Protease Activity of a 90-kDa Protein Isolated from Scallop Shells

We have previously reported the free radical scavenging activity of a protein with a molecular weight of 90 kDa (90kDa protein) isolated from the scallop shell. In this study, we found that the 90-kDa protein also shows protease activity. The protein was most active at an alkali pH and at 60 degrees C, and its activity was inhibited by serine protease inhibitors, phenylmethylsulfonyl fluoride and diisopropyl fluorophosphate. Its activity was maintained at approximately 90% of the initial activity, even in the presence of denaturants such as 1% sodium dodecyl sulfate (SDS) and 6 M urea. Substrate specificity analysis performed using synthetic peptides showed that the 90-kDa protein cleaves preferentially at Lys-X and Arg-X bonds. A portion of Phe-X bond was also cleaved by the 90-kDa protein. When casein was treated with the 90-kDa protein, it was digested at the Arg-X, Lys-X, and Phe-X bonds. The 90-kDa protein may be useful for proteome analysis because it retains its activity even in the presence of 1% SDS. To the best of our knowledge, this is the first report of a protease found in scallop shell.