[Study of the role of mitochondrial creatine phosphokinase isoenzyme in the process of energy transport in cardiac cells].

The kinetic properties of creatinephosphokinase connected with the mytochondria of the heart were studied. The following kinetic parameters were measured: the Michaelis constants for all substrates -- MgATP, MgADP, creatine and creatinephosphate, and the maximal reaction rates for the direct and reverse reactions catalized by the mytochondrial iso-enzyme of creatinephosphokinase. The peculiarity of this iso-enzyme was demonstrated to consist in the independence of binding adeninenucleotides and guanidine substrates. The kinetic characteristics of this iso-enzyme are such that ATP synthesis from ADP and creatinephosphate is preferable: the Michaelis constant for MgADP is 0.05 mM, for creatinephosphate -- 0.5 mM, for MgATP -- 0.7 mM, for creatine -- 5.0 mM. It was also demonstrated that in the presence of all substrates and products of the reaction the ratio of the speeds of the direct and reverse reactions is regulated by Mg ions: with a low concentration of Mg (below that of ATP) the reaction of creatinephosphate synthesis takes place, with the Mg concentration growing the speed of ATP synthesis increases. Thus, an increase of Mg concentration can, depending on the conditions of the reaction, result in its complete reversal. The regulatory role of Mg is also demonstrated for the case in which ATP is synthesized in the reaction of oxidative phosphorylation, creatinephosphokinase-controlled reaction.