Effects of endogenous cathepsins B and L on degradation of silver carp (Hypophthalmichthys molitrix) myofibrillar proteins

The activities of cathepsins B and L in minced silver carp meat were 4.89 and 3.81 units/g, respectively. About 11.30% activity for cathepsin B and 25.61% activity for cathepsin L were left after washing with distilled water, suggesting a short wash removed a large portion of both cathepsins B and L, but the activities of cathepsins still remained to some extent, and the remaining activity of cathepsin L was higher than that of cathepsin B. Higher cathepsin residual activity was correlated with the autolytic rate of myosin heavy chain (MHC) during the autolysis of myofibrillar proteins at 50C. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis indicated that both of the purified cathepsins B and L could result in significant degradation of MHC at 50 and 35C, which was close to the temperature of gel softening and setting, respectively, but cathepsin L seemed to be a key proteinase for hydrolyzing the myofibrillar protein.