Detection of a trypsin-like serine protease and its endogenous inhibitor in hake skeletal muscle.

When dialyzed extracts from hake (Merluccius hubbsi) skeletal muscle were chromatographed in DEAE-Sephacel, an alkaline protease (37 degrees C, pH 8.5) and a trypsin inhibitor were isolated. The enzyme showed its maximal activity against azocasein in the range of pH between 7 and 9. The protease was able to hydrolyze the trypsin substrates Bz-Arg-OEt and Tos-Arg-OMe and did not cleave the chymotrypsin substrate Bz-Tyr-OEt. The enzyme was strongly inhibited by several serine protease inhibitors, whereas inhibitors of the other types of proteases scarcely affected it. The protease was able to degrade the major contractile and cytoskeletal constituent proteins of myofibrils and to accumulate acid-soluble products. The protease activity was completely suppressed by the addition of the trypsin inhibitor isolated from the same muscle. These results indicate that hake skeletal muscle contains a trypsin-like serine protease which might be involved in the catabolism of myofibrillar proteins, as well as in the proteolytic events that take place during post mortem storage of fish muscle.