Elevated Activity of Cathepsin L-like Protease in the Jellied Meat of Japanese Flounder.

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The cause of the jelification of Japanese flounder meat was investigated. Infection by parasites was not histologically detected, while the arrangement of myofibrils was notably disturbed. Large amounts of trichloroacetic acid soluble materials and a breakdown of myosin heavy chain suggested the occurrence of proteolytic degradation in the jellied meat.Crude extract of the jellied meat showed proteolytic activity on myosin heavy chain, which was hardly detected in the normal meat. The extract hydrolyzed Z-Phe-Arg-MCA most preferentially among the synthetic peptide substrates tested. Activities on myosin heavy chain and Z-Phe-Arg-MCA were inhibited by leupeptin, antipain, and E-64, but not by soybean trypsin inhibitor or pAPMSF (a specific inhibitor for trypsin-like proteases), suggesting that the activities were ascribed to a cysteine protease(s). Both myosin heavy chain and Z-Phe-Arg-MCA hydrolyzing activities were co-eluted from TSK G3000SWXL column at an eluting position whose molecular weight corresponded to 34, 000. Together with these results, the protease activity elevated and possibly involved in the jelification of Japanese flounder meat was taken to be due to an endogenous cathepsin L-like protease.