Kinetic Study of the Activation Process of β‐Galactosidase from Escherichia coli by Mg2+

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Abstract
The action of Mg2+ 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 Mg2+ ions, a residual activity has been found and the catalytic properties of Mg2+‐free enzyme have been determined.The activation process induced by Mg2+ is a slow process, the rate of which depends on the Mg2+ concentration. The deactivation process obtained by adding EDTA is also a slow process. Activation by Mg2+ is not a cooperative process. The apparent dissociation constant of the Mg2+ 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 Mg2+ 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.