Molecular Pharmacology, Vol 9, 405-413, Copyright © 1973 by the American Society for Pharmacology and Experimental Therapeutics

Effect of Perfusion with Different Substrates and with Isoproterenol on Phosphofructokinase Activity in the Isolated Guinea Pig Heart

¹ Department of Pharmacology, Stanford University School of Medicine, Stanford, California 94305

Guinea pig hearts were perfused with Krebs-bicarbonate solution to which glucose, pyruvate, acetate, -hydroxybutyrate, or octanoate was added. Heart extracts were prepared in the presence of 13 mM caffeine and assayed for phosphofructokinase activity. When assays were done at pH 6.9 (a pH which allows demonstration of allosteric regulation), extracts from glucose-perfused hearts had high enzyme activity, while extracts from pyruvate-, -hydroxybutyrate-, and octanoate-perfused hearts had very low activity. Extracts from acetate-perfused hearts had intermediate activity. The reduction in phosphofructokinase activity in pyruvate-perfused hearts was correlated with increased tissue citrate levels. Furthermore, when enzyme activity was determined as a function of fructose-6-P concentration, a sigmoid curve was obtained for extracts of pyruvate-perfused hearts and a hyperbolic curve was obtained for extracts of glucose-perfused hearts. Addition of isoproterenol to the perfusate antagonized the effect of pyruvate. The data provide direct evidence for allosteric control of the enzyme in intact tissue by intermediary metabolites of aerobic metabolism.