Thermal stability of myosin and protective effect of F-actin on myosin affect the thermal inactivation of calcium-ATPase in unstable kuruma prawn myofibrils

Abstract

The thermal stability of myosin and the protective effect of F-actin on myosin in kuruma prawn myofibrils were investigated from the thermal inactivation rates at 25\xa0°C of Ca-ATPase in myosin and myofibrils at various concentrations of KCl. The thermal inactivation rate constant (kD) of myofibrillar Ca-ATPase increased with increasing KCl concentration; however, the thermal inactivation followed a biphasic first-order reaction regardless of the KCl concentration: a relatively fast inactivation rate in the earlier phase (kDe) followed by a slower inactivation rate in the later phase (kDl) of the heat treatment. The thermal inactivation of myosin at various concentrations of KCl or sorbitol also followed a biphasic first-order reaction, and the differences between the kDe and kDl of myosin were always about twofold. kDe and kDl of myosin at 0.1\xa0M KCl were decreased to 1/6 and 1/13, respectively, by the binding action of F-actin. These results suggest that the thermal stability of myosin and the protective effect of F-actin affect the stability and thermal inactivation of kuruma prawn myofibrils at physiological ionic strength.