Kinetic Study of the Activation Process of β‐Galactosidase from <i>Escherichia coli</i> by Mg²⁺

Abstract

The action of Mg 2+ ions on β‐galactosidase activity has been studied under strictly controlled conditions with different substrates. The activation effect does not depend on the substrate. In the absence of Mg 2+ ions, a residual activity has been found and the catalytic properties of Mg 2+ ‐free enzyme have been determined. The activation process induced by Mg 2+ is a slow process, the rate of which depends on the Mg 2+ concentration. The deactivation process obtained by adding EDTA is also a slow process. Activation by Mg 2+ is not a cooperative process. The apparent dissociation constant of the Mg 2+ enzyme complexe is rather small, 0.65 ± 0.05 μM. The kinetics of activation and deactivation have been studied with phenyl galactoside as substrate. The results indicate that activation by Mg 2+ operates through a binding with free enzyme. This binding involves at least two steps: the first and more rapid one is a single metal‐protein binding, the following slow step probably involves a conformational change of the enzyme induced by the metal binding.