Effects of sodium gluconate on thermal denaturation and solubilization of carp myofibrils

The effects of sodium gluconate (Na-gluconate) on thermal inactivation of C a-ATPase and solubilization of carp myofibrils were compared with those of sorbitol and sodium chloride (NaCl). Na-gluconate decreased the thermal ina ctivation rate constant for myofibrillar Ca-ATPase (k(D)) the same as sorbi tol did. On the contrary, NaCl accelerated thermal denaturation of myofibri ls. The protective effect (E value) of Na-gluconate on heat-denaturation wa s considerably larger than that of sorbitol. Although sorbitol had no effec t on the solubilization of myofibril, the addition of 0.25 -0.30 M Na-gluco nate induced a decrease in turbidity of myofibril suspension accompanied by the increase in the amount of extracted protein. Therefore, it was clearly demonstrated that Na-gluconate solubilized myofibrils at higher concentrat ion than NaCl. The measurement of sodium ion concentration in the solution with a sodium ion electrode indicated less electrolytic dissociation degree of Na-gluconate than NaCl, suggesting that the myofibrils solubilizing eff ect of both compounds corresponded to their ionization degree in the soluti on.