Stable isotopes of Mg2+ as activators of the suppressed ATP-generating function of mitochondria]

The ATP-generating activity of rat myocardial mitochondria and intramitochondrial creatine kinase was examined as a function of the isotopy of the incubation medium magnesium pool. The study was performed using in vitro systems prepared from the hearts of animals injected with I-methylnicotine amide, which suppresses the NAD (NADP)-dependent reactions in vivo. It was shown that the presence of the Mg-25 paramagnetic cations essential by compensates for the intramitochondrial ATP deficiency caused by the I-methyl-nicotine amide-induced blockade of oxidative phosphorylation. This effect is hardey achievable in systems where the magnesium pool consists of isotopes with a zero nuclear spin (Mg-24,Mg-26). The restoration of mitochondrial ATP synthesis involves the participation of creatine kinase since the activity of the latter does not depend on I-methyl-nicotine amide. In this case, the high efficiency of this restaration seems to be a spin-selective phenomenon which requires predominantly Mg-25(2+) cations. A possible meaning of the data for further studies on the mechanisms of enzymatic catalysis regulation is discussed.