ABSTRACT
The rates of adenosine triphosphate (ATP) production by isolated mitochondria and mitochondrial creatine kinase incubated in isotopically pure media containing, separately, (24)Mg(2+), (25)Mg(2+), and (26)Mg(2+) ions were shown to be strongly dependent on the magnesium nuclear spin and magnetic moment. The rate of adenosine 5'-diphosphate phosphorylation in mitochondria with magnetic nuclei (25)Mg is about twice higher than that with the spinless, nonmagnetic nuclei (24,26)Mg. When mitochondrial oxidative phosphorylation was selectively blocked by treatment with 1-methylnicotine amide, (25)Mg(2+) ions were shown to be nearly four times more active in mitochondrial ATP synthesis than (24,26)Mg(2+) ions. The rate of ATP production associated with creatine kinase is twice higher for (25)Mg(2+) than for (24,26)Mg and does not depend on the blockade of oxidative phosphorylation. There is no difference between (24)Mg(2+) and (26)Mg(2+) effects in both oxidative and substrate phosphorylation. These observations demonstrate that the enzymatic phosphorylation is a nuclear spin selective process controlled by magnetic isotope effect. The reaction mechanism proposed includes a participation of intermediate ion-radical pairs with Mg(+) cation as a radical partner. Therefore, the key mitochondrial phosphotransferases work as a magnesium nuclear spin mediated molecular machines.
Subject(s)
Adenosine Diphosphate/metabolism , Adenosine Triphosphate/metabolism , Magnesium/metabolism , Mitochondria, Heart/metabolism , Nuclear Magnetic Resonance, Biomolecular/methods , Radioisotope Dilution Technique , Adenosine Diphosphate/chemistry , Adenosine Triphosphate/chemistry , Animals , Biochemistry/methods , Cells, Cultured , Isotopes/analysis , Isotopes/chemistry , Isotopes/metabolism , Magnesium/analysis , Magnesium/chemistry , Male , Models, Biological , Models, Chemical , Phosphorylation , Rats , Spin LabelsABSTRACT
Phosphoglycerate kinase (PGK) is found to be controlled by a (25)Mg(2+)-related magnetic isotope effect. Mg(2+) nuclear spin selectivity manifests itself in PGK-directed ADP phosphorylation, which has been clearly proven by comparison of ATP synthesis rates estimated in reaction mixtures with different Mg isotopy parameters. Both pure (25)Mg(2+) (nuclear spin 5/2, magnetic moment +0.85) and (24)Mg(2+) (spinless, nonmagnetic nucleus) species as well as their mixtures were used in experiments. In the presence of (25)Mg(2+), ATP production is 2.6 times higher compared with the yield of ATP reached in (24)Mg(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 (25)Mg(+) radical cation and phosphate oxyradical are involved.
