Effect of heat on the kinetic constants of myosin-adenosine triphosphatase.

Nanninga and Mommaerts used the firefly technique for detection of adenosine triphosphate (ATP) in order to establish the binding of ATP to myosin1. The addition of creatine phosphate and creatine phosphate transphosphorylase is necessary to counteract the hydrolysis of ATP by the myosin. In this way a maximal binding of 1 mole ATP to 1 mole myosin was established while it was also possible to determine k1, the kinetic constant of the formation of the ATP–myosin complex, from the initial speed of disappearance of the free ATP as measured from the decrease of the luminescence2. The k1 determination can be done in absence of the rephosphorylating system. The effect of heat inactivation of the myosin on both the k1 and on the bound ATP was studied. The myosin was 1.31 per cent, dissolved in 0.3 M potassium sulphate, 0.01 M tris-buffer of pH 7.0 and was heated for 90 min. at 37° C. Then it was added to the luciferin–luciferase solution at different ATP concentrations. It was found that both k1and the bound ATP decrease about sevenfold (Table 1).