Magnesium magnetic isotope effect: A key to the mechanochemistry of phosphorylating enzymes as molecular machines

The discovery of the powerful magnesium isotope effect on enzymatic ATP synthesis provides a new insight into the mechanochemistry of enzymes as molecular machines. The catalytic activities of ATPase, creatine kinase, and glycerophsphate kinase containing a Mg2+ ion with magnetic isotope nuclei (25Mg) were found to be two to four times higher than those of the enzymes with spinless, nonmagnetic magnesium cation isotopes (24Mg or 26Mg). This demonstrates unambiguously that ATP synthesis is a spin-selective process involving Mg2+ as the electron-accepting reagent. ATP synthesis proceeds in an ion-radical pair consisting of an ADP oxyradical and Mg2+. In this process, the magnesium bivalent cation is the key agent that transforms the mechanics of a protein molecule into chemical processes. This ion is the crucial structural component of enzymes as mechanochemical molecular machines.