Abstract
The protective effect of ATP-MgCl2 on the thermal denaturation of rabbit and tilapia myosins was studied by measuring the change in its Ca-ATPase activity. When myosin (0.5M KCI, pH 7.5) was incubated in the presence of varied concentrations (0-1.0mM) of ATP-MgCl2, Ca-ATPase activity changed in two steps: an early unchanged stage, followed by a rapid inactivation stage. The time required for inducing the rapid inactivation of Ca-ATPase was equal to the time needed for most of the ATP hydrolyzed in the medium. When myosin was incubated in the presence of a fixed concentration of ATP-MgCl2 with ATP-regenerating system (phosphoenol pyruvate plus pyruvate kinase), Ca-ATPase was slowly inactivated in a single first order process and the inactivation rate was decreased as the con-centration of ATP-MgCl2 increased (0-0.3mM). It was thus found that the rate decreased to one-tenth of the initial value upon addition of 0.1mM ATP-MgCl2. In addition, the protective effect of ATP-MgCl2 against thermal inactivation was much stronger for the myosin in 0.1M KCI-medium than for that in the O.5M KCI-medium. The protective effect of ATP-MgCl2 on the denaturation of myofibrillar protein in pre-rigor fish muscle was discussed.
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