Phosphoryl transfer reactions rate acceleration

Mg2+ is associated with a large number of enzymes involving the hydrolysis and transfer of phosphates. The MgATP complex serves as the substrate in many cases. As noted in Section 62.1.2.2.2, the interaction of Mg2+ with the ATP enhances the transfer (to a substrate or water) of the terminal phosphoryl group. The results of many studies with model compounds lead to the postulate of an SN2 mechanism for this reaction.125 Associative pathways allow greater control of the stereochemistry of the substitution, and the rates of such processes are accelerated more effectively by metal ions. 

The rate of formation of the phosphoenzyme and the K -dependent rate of breakdown are sufficiently fast to allow the phosphoenzyme to be an intermediate in the overall ATPase reaction. The initial step is the reversible binding of ATP to the enzyme in the absence of added K ion, followed by a Mg - (and proton-) dependent transfer of the terminal phosphate of ATP to the catalytic subunit (ErP H ). The Mg remains occluded until dephosphorylation. Increasing the hydrogen ion concentration on the ATP-binding face of the vesicles accelerates phosphorylation, whereas increasing the potassium ion concentration inhibits phosphorylation. Increasing the hydrogen ion concentration reduced K inhibition... 

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