Equilibrium and kinetic studies of the pyruvic kinase reaction.

or indirectly by a multienzyme system consisting of malic enzyme, malic dehydrogenase, and phosphoenolpyruvic carboxykinase (2, 3). However, the physiological significance of these two possible pathways has not been established. Lardy and Ziegler (4) demonstrated that the pyruvic kinase reaction is reversible in the presence of potassium and Meyerhof and Oesper (5) determined the apparent equilibrium constant of the reaction and obtained an average value of 1960 f 475 at an unspecified alkaline pH and 30”. This paper presents further studies on the pyruvic kinase reaction including values for the equilibrium constant as a function of pH, the Michaelis constants for the reaction components, and maximal initial velocities for the forward and back reactions. These data when supplemented by other studies may be useful in attempts to evaluate the contribution of the pyruvic kinase reaction to the biosynthesis of phosphopyruvate.