[Creatine phosphate synthesis coupled to glycolytic reactions in heart cell cytosol]

It is shown that a cytosolic fraction of proteins from rat heart, containing all glycolytic enzymes and creatine phosphokinase (CPK) in natural proportions, catalyses in the presence of creatine (Cr) the intensive creatine phosphate (CP) synthesis coupled to glycolytic depletion of glucose, fructose-1,6-diphosphate (FDP) and phosphoenolpyruvate (PEP). The ratio of CP to lactate produced was 1.0 in the case of PEP as glycolytic substrates. In the CP production process the CPK reaction was not the rate limiting step: the mass action ratio for CPK was equal to the apparent equilibrium constant for this reaction, and the maximal rate of the CPK reaction exceeded the observed rate of glycolysis by a factor 6. It is concluded that in such a system the components of the CPK reaction are in quasiequilibrium and the mechanism of CP synthesis can be considered to be a continuous decrease in ADP concentration due to its phosphorylation in the glycolytic reactions, ATP concentration being constant due to its continuous utilization and resynthesis, this leading to an increase in CP concentration. The possible role of the CPK system in regulation of glycolysis in muscle cells is discussed.