Abstract
In the isolated, perfused Rana ridibunda heart, the concentrations of the metabolites were measured as a function of time, under increased heart work. The changes in tissue contents of adenine nucleotides were time dependent. ADP, AMP, and inorganic phosphate levels increased simultaneously, while ATP and creatine phosphate levels decreased. The tissue contents of hexose monophosphates and citrate decreased and contents of fructose bisphosphate, lactate, and pyruvate rose. A comparison of mass action ratios with apparent equilibrium constants for the glycolytic reactions indicated that phosphoglucose isomerase, aldolase, triosephosphate isomerase, and lactate dehydrogenase reactions are close to equilibrium, while phosphofructokinase is displaced from equilibrium. During increased heart work, changes in the tissue contents of adenine nucleotides and citrate appeared to play a role in the regulation of glycolysis at the level of phosphofructokinase activity. From the results, it appears that in amphibian heart, glycolysis seems to be similar to that of mammalian heart as far as control is concerned, in spite of its structural and functional differences.
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