Activation and inhibition of myosin B adenosine triphosphatase by Mg ++ and Ca ++ at low concentration of KCl

Abstract

Rabbit skeletal myosin B was used to examine the effects of Mg ++ and Ca ++ on the adenosine triphosphatase (ATPase) activity at low concentrations (0.018–0.198 M) of KCl. A simple mechanism that assumes the binding of divalent cations with myosin B was shown to explain the activation and inhibition of activity caused by Mg ++, and the Ca-activation in the presence of Mg ++ at varied concentrations of KCl. For the binding reaction by which Mg ++ activates the ATPase, the apparent dissociation constant at 0.018 M KCl (pH 7.4) and the number of Mg ++ binding sites per gram of myosin B were calculated from the kinetic experiments as 0.25–0.35 μ M and 1.5–5.5 μq, respectively.