Phosphate Transfer Enzymes as the Nuclear Spin Selective Nanoreactors

Abstract

Magnesium isotope effect manifests itself in the enzymatic ATP synthesis at relatively high concentrations of Mg2+ ions. At low concentrations, there is no isotope effect at all so the nucleophylic mechanism of the ATP synthesis dominates. Concentration of Mg2+ ions exceeds intracellular one by 50-100 times, a huge isotope effect appears which means that the new ion-radical mechanism of ATP synthesis is switched on. This provides an additional and considerable source of ATP. This mechanism implies the electron transfer from Mg2+(ADP) complex to the Mg(H2O)n2+ complex generating an ion-radical pair as a starting reaction of the ATP synthesis. Populations of both singlet and triplet states and the rate of singlet-triplet conversion in the pair are controlled by hyperfine coupling of the unpaired electrons with magnetic 25Mg and 31P nuclei and by Zeeman interaction. Due to these two interactions, the yield of ATP is a function of nuclear magnetic moment and magnetic field. Electron transfer reaction does not depend on m but strongly depends on n. It is exoergic and energy allowed at (0 £ n << ¥) for the deprotonated pyrophosphate anions and at (0 £ n < 4) for the protonated ones; for other values of n, the reaction is energy deficient and forbidden. The boundary between exoergic and endoergic regimes corresponds to the trigger magnitude n* (n* = 4 for protonated anions and 6 < n* << ¥ for deprotonated ones). These results explain why the ATP synthesis occurs only in some special nanodevices, i.e., within a very few molecular enzymatic machines, but not in water (n = ¥). Biomedical and biotechnological consequences of the ion-radical enzymatic ATP synthesis as well as its protein (catalytic site) nanotopology background are under discussion.