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The production of ATP in mitochondria depends on the magnesium nuclear spin and magnetic moment of a Mg2+ ion in creatine kinase and ATPase. This suggests that enzymatic synthesis of ATP is an ion-radical process and thus depends on the external magnetic field (magnetobiology originates from this fact) and microwave fields, which control the spin states of ion-radical pairs and affect the ATP synthesis. The chemical mechanism of ATP synthesis and the origin of biological effects of electromagnetic (microwave) fields are discussed.

A discovery of the huge magnesium isotope effect in enzymatic ATP synthesis provides a new insight into mechanochemistry of enzymes as the molecular machines. It has been found that the catalytic activity values of ATPase, creatine kinase and phosphoglycerate kinase are 2 to 4-fold higher once their active sites contain magnetic (25Mg) not spinless, non-magnetic (24Mg, 26Mg), magnesium cation isotopes. This clearly proves that the ATP synthesis is a spin-selective process involving Mg2+ as the electron accepting reagent. The formation of ATP takes place in an ion-radical pair resulted by two partners, ATP oxyradical and Mg+. The magnesium bivalent cation is a key player in this process, this ion transforms the protein molecule mechanics into a mere chemistry. This ion is a most critical detail of structure of the magnesium dependent phosphorylation enzymes as the mechanochemical molecular machines.

The functional role of particulate MM isozyme of creatine phosphokinase (CPK) bound to heart myofibrils has been studied. It has been shown that in the presence of heart myofibrils and MgATP creatine phosphate can be used to rephosphorylate ADP formed in the MgATPase reaction. The rate of creatine phosphate splitting is determined by the kinetic properties of myofibrillar MgATPase and by the kinetic parameters of myofibrillar CPK. It has been found that a purified heart plasma membrane preparation contains high CPK activity. CPK isozyme bound to plasma membrane of heart cells is identical to MM isozyme of CPK and is able to rephosphorylate effectively ADP, formed in the (Na K)ATPase reaction. The rate of creatine phosphate splitting in these coupled reactions is sensitive to ouabain and is determined by the kinetic parameters both of the (Na, K)ATPase and plasma membrane CPK. The results obtained indicate the important role of myofibrillar and plasma membrane CPK in the intracellular energy transport processes.

The method of the penetrating ions allows to observe the creatine phosphokinase function of heart mitochondria in steady state conditions. The addition of ADP to respiring mitochondria decreases the membrane potential in the course of the ATP synthesis. The subsequent addition of creatine decreases the membrane potential for a long period of time because of ADP formation in creatine phosphokinase reaction. It was shown in the experiments with maintainance of the constant concentration of ADP or ATP in the medium that the ADP concentration in the medium acts mainly on the membrane potential during the creatine phosphate synthesis. There is no effect of creatine on the membrane potential of liver mitochondria which have no creatine phosphokinase.

It has been shown that the contents of mitochondria and mitochondrial isoenzyme of creatine phosphokinase are almost identical in skeletal and heart muscles. In mitochondria from both types of muscle creatine phosphokinase is functionally coupled to ATP-ADP translocase. This kind of coupling ensures complete conversion of mitochondrial ATP energy into the energy of creatine phosphate and effective control of oxidative phosphorylation by the creatine phosphokinase reaction. It has also been shown that all isoenzymes of creatine phosphokinase from heart and skeletal muscle have very similar kinetic properties. Significant differences have been found to exist between isoenzyme patterns of these muscles and also in distribution of different isoenzymes in the cells. In skeletal muscle cells creatine phosphokinase is present mainly as cytosolic MM isoenzyme; about 6% of total cellular activity is localised also in mitochondria. Due to high activity of cytosolic isoenzyme the total activity of creatine phosphokinase is about three times higher in skeletal muscle than in cardiac muscle. It has been also shown that phosphoenolpyruvate and glucose-6-phosphate do not have any inhibitory effect on creatine phosphokinase.