The synthesis of creatine phosphate (CP) by mitochondrial creatine kinase during oxidative phosphorylation was terminated when the mass action ratio of the creatine kinase reaction Γ = [ADP]·[CP][ATP]·[Cr] became equal to the apparent equilibrium constant (Keqapp) of this reaction. Subsequent excess of Γ over the Keqapp was due to an increase in the ADP concentration in the medium. A comparable increase in the ADP concentration also occurred in the absence of creatine (Cr) in the incubation medium. Increase in the ADP concentration was shown to be associated with a decrease in the rate of oxidative phosphorylation and with a relative increase in the ATPase activity of mitochondria during the incubation. A low concentration of ADP (<30 μM) and relatively high concentrations (1-6 mM) of other components of the creatine kinase reaction prevented the detection of the reverse reaction within 10 min after Γ exceeded the Keqapp, but the reverse reaction became evident on more prolonged incubation. The reverse reaction was accompanied by a further increase in Γ. Low ADP concentration in the medium was also responsible for the lack of an immediate conversion of the excess creatine phosphate added although Γ > Keqapp. The findings are concluded to be in contradiction with the concept of microcompartment formation between mitochondrial creatine kinase and adenine nucleotide translocase.
