Elucidation of Factors Responsible to Raise Dependency of Mg-ATPase Activity of Myofibrils on KCl Concentrations during Meat Conditioning

抄録

In order to clarify factors inducing the changes in the Mg-ATPase activity of myofibrils during meat conditioning, we treated myofibrils in vitro with various muscle proteinases and Ca2²⁺. Ca²⁺ or proteasome did not change the Mg-ATPase activity at 25°C and pH5.5 or 7.0. m-Calpain enhanced the dependency of the Mg-ATPase activity of myofibrils on KCl concentrations (DAAK) in the range of 0 to O.05M KCl at 25°C and pH7.2 as similarly as observed during meat conditioning, but did not at pH5.5. Therefore, m-calpain was assumed to contribute to the increase in DAAK in the early stage of meat conditioning, i. e., before the pH of muscle declined to the ultimate pH. Crude cathepsins raised DAAK in the range of 0 to 0.1M KCl at 25°C and both pH5.5 and 7.0. As a result of the chromatographic separation, cathepsins D and L were shown to enhance DAAK remarkably. Although cathepsins B and H alone raised DAAK only a little, their action was enhanced by the coexistence of cathepsin L. During meat conditioning cathepsins D and L are thus considered to contribute to the increase in DAAK involving a synergistic action of cathepsins B and H. However, all these proteinases investigated here did not cause so much remarkable increase in the maximum value of the Mg-ATPase activity of myofibrils occurring at low KCl concentrations as observed during meat conditioning, suggesting the existence of other unknown factors inducing such changes.