Some Kinetic Properties of Liver Pyruvate Kinase (Type L)

Abstract

Abstract Type L pyruvate kinase from mouse liver has been studied. The enzyme is strongly inhibited by low concentrations of copper ions, and the inhibition is reversed by fructose 1,6-diphosphate. In the absence of inhibitor, fructose 1,6-diphosphate also increases the pyruvate kinase activity at pH values higher than 7. Furthermore, the Cu++ inhibition is pH and K+ concentration dependent. Plots of reaction rates against phosphoenolpyruvate concentration give a sigmoid curve whereas a hyperbolic curve is obtained for the other substrate (adenosine diphosphate). When fructose 1,6-diphosphate is added, the response to phosphoenolpyruvate concentration is transformed to give a Michaelian curve and the affinity of the enzyme for this substrate increases. In the presence of Cu++, the Km for adenosine diphosphate is not substantially modified, but the Vmax decreases markedly. On the other hand, the apparent Km for phosphoenolpyruvate is considerably increased by this cation. The enzyme has a full requirement for Mg++ and a monovalent cation (K+ or NH4+). The activation of the enzyme with NH4+ has been found to be more efficient than with K+. The physiological role of the Cu++-fructose 1,6-diphosphate interrelation in the balance between glycolysis and gluconeogenesis is discussed.