Spin biochemistry -: Magnetic 24Mg 25Mg 26M isotope effect in mitochondrial ADP phosphorylation

The rates of adenosine triphosphate (ATP) production by isolated mitochondria and mitochondrial creatine kinase incubated in isotopically pure media containing, separately, Mg-24(2+), Mg-25(2+), and Mg-26(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 Mg-25 is about twice higher than that with the spinless, nonmagnetic nuclei Mg-24,Mg-26. When mitochondrial oxidative phosphorylation was selectively blocked by treatment with 1-methylnicotine amide, Mg-25(2+) ions were shown to be nearly four times more active in mitochondrial ATP synthesis than Mg-24,26(2+) ions. The rate of ATP production associated with creatine kinase is twice higher for Mg-25(2+) than for Mg-24,Mg-26 and does not depend on the blockade of oxidative phosphorylation. There is no difference between Mg-24(2+) and Mg-26(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.