Some Kinetic Properties of Liver Pyruvate Kinase (Type L)

Abstract

Abstract Type L pyruvate kinase from rat liver has been further studied with a more purified preparation (about 400- to 600-fold). The enzyme has an absolute requirement for a monovalent cation (K+ or NH4+). At pH 7.5, there is a sigmoidal velocity response with respect to both univalent cations. In the presence of fructose 1,6-diphosphate or at saturating concentration of phosphoenolpyruvate, the response to K+ concentration is transformed to give a Michaelian curve. On the other hand, K+ has only a slight heterotropic effect on the homotropic cooperativity of the substrate (phosphoenolpyruvate) and of the inhibitor (ATP). The pH exerts a complex influence on the K+ activation kinetics. At acid (6.0) or at very alkaline (8.35) pH values, the cooperativity of K+ decreases markedly. The effect of Mg++ concentration on enzyme activity was also studied.