Magnetic-Isotope Effects of Magnesium and Zinc in Enzymatic ATP Hydrolysis Driven by Molecular Motors

Abstract

The effects of different magnesium and zinc isotopes on the enzyme activity of myosin subfragment-1 have been explored. The rate of the enzymatic ATP hydrolysis in reaction media enriched with the magnetic isotope, 25Mg, is twice as high as it is in reaction media enriched with the nonmagnetic isotopes, 24Mg or 26Mg. A similar effect of nuclear spin catalysis has been detected in the experiments with zinc isotopes as cofactors of the enzyme. The rate of the enzymatic ATP hydrolysis with magnetic 67Zn increases by 40–50% compared to that with nonmagnetic 64Zn or 68Zn. The magnetic-isotope effects have been observed at the physiological concentration of magnesium and zinc chlorides (5 mM). The catalytic effect of the magnetic magnesium isotope 25Mg has been revealed in the experiments with Mg-dependent ATPase of myometrial plasma membranes. The magnetic-isotope effects indicate that there is a spin-selective rate-limiting step in the chemo-mechanical process driven by the “molecular motor” due to the energy of ATP hydrolysis and that nuclear spin catalysis causes acceleration of this stage. Some possible mechanisms of the nuclear spin catalysis are discussed.