Characterization of proteolytic activity in octopus (Octopus vulgaris) arm muscle

A new proteolytic activity assay was devised to avoid the interference of paramyosin which causes gelling during the enzymatic assay. Extremely high autolytic activity was observed in octopus arm muscle, which was 40-500 fold higher than those of various other fish species. The proteinase was inhibited strongly by leupeptin and iodoacetic acid and, to a lesser degree, by trans-epoxysuccinyl-L-leucylamino (4-guanidono)butane (E-64), indicating the class as a thiol proteinase. The proteinase exhibited optimum activity at pH2.5 and 40C, although it contained a sulfhydryl group in the active site. Myosin heavy chain was the primary myofibrillar protein which was hydrolyzed during the autolysis of octopus arm followed by paramyosin. Actin showed no signs of hydrolysis during the incubation of up to 8 h. Due to ifs high affinity for myosin, the enzyme activity should be controlled during processing octopus to ensure the functionality of myosin.