Magnetic isotope effect of magnesium in phosphoglycerate kinase phosphorylation

Phosphoglycerate kinase (PGK) is found to be controlled by a Mg-25(2+)-related magnetic isotope effect. Mg2+ nuclear spin selectivity manifests itself in PGK-directed ADP phosphorylation, which has been clearly proven by comparison of ATIP synthesis rates estimated in reaction mixtures with different Mg isotopy parameters. Both pure Mg-25(2+) (nuclear spin 5/2, magnetic moment +0.85) and Mg-24(2+) (spinless, nonmagnetic nucleus) species as well as their mixtures were used in experiments. In the presence of Mg-25(2+), ATP production is 2.6 times higher compared with the yield of ATP reached in Mg-24(2+)-containing PGK-based catalytic systems. The chemical mechanism of this phenomenon is discussed. A key element of the mechanism proposed is a nonradical pair formation in which Mg-25(+) radical cation and phosphate oxyradical are involved.