Involvement of cathepsins B and L in the post-mortem autolysis of mackerel muscle

The intracellular distributions of catheptic enzymes (cathepsins) in white muscle of mackerel were investigated using differential centrifugation. The enzymes included cathepsin B, cathepsin L, beta-N-acetylglucosaminidase, and cathepsin D (a lysosomal marker), and alkaline phosphatase (a microsomal marker). The highest relative specific activities of each of the cathepsins and beta-N-acetylglucosaminidase were in the lysosomal fraction, and the highest relative specific activity of alkaline phosphatase was in the microsomal fraction. The buoyant density of white muscle lysosomal particles ranged from 1.03 to 1.10 g ml(-1). In ageing muscle at 0 degrees C, the activities of cathepsins B and L gradually decreased in the lysosomal fraction, while they increased in the supernatant fraction. Mackerel cathepsin L hydrolyzed myosin, troponin T, troponin I, and tropomyosin. Mackerel cathepsin B did not hydrolyze any of the myofibrils from mackerel white muscle. These results suggested that the main cause of post-mortem degradation of mackerel muscle tissue was due to the activity of cathepsin L. (C) 1998 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.