Activation of the F₁-ATPase in mitochondria of Vigna unguiculata (L.)Walp. cv. Pitiuba by K⁺

Abstract

Mitochondria from the bean Vigna unguiculata contain an ATPase system that is strongly activated by K+ and Na+ in the presence of low concentrations of substrate. Optimum activation by physiological concentrations of K+ is achieved in the presence of 0.1 mM MgATP. At the substrate optimum of the total ATPase, which is 2.3 mM, the enzyme is only poorly activated by K+. The K+-activated component of the total F1-ATPase behaves like an individual enzyme with kinetic properties different to the total F1-ATPase. On the basis of enzyme kinetic measurements, we determined the mechanism of activation by K+ as follows:[Formula: see text]K+ is not required for the binding of the substrate MgATP to the enzyme but for the splitting of the enzyme–substrate complex into the reaction products.