Proteolytic enzymes of squid mantle muscle

1. 1. The profiles of the proteolytic activity in autolysis of the mantle muscle of the squid, Ommastrephes sloani pacificus , was studied by measurement of the released peptides and by SDS polyacrylamide gel electrophoresis. 2. 2. In the acidic ranges, there was found high proteolytic activity with a maximum at pH 3.1. This activity was ascribed to a cathepsin D-like proteinase. 3. 3. The activity above the neutral pH was much lower than that of the acid proteinases, and appeared to be due to metallo- and thiol-proteinases.