Feed-forward activation and feed-back inhibition of pyruvate kinase type L of rat liver

Crystalline type L pyruvate kinase was activated by fructose-1,6-diphosphate. The Michaelis constant for phosphoenolpyruvic acid decreased to about one tenth and the maximum velocity was doubled by the presence of fructose-1,6-diphosphate. The activity of type M pyruvate kinase was not influenced significantly by fructose-1,6-diphosphate. The sensitivity to ATP inhibition of type L enzyme was decreased very markedly by fructose-1,6-diphosphate. Liver type L enzyme became completely insensitive to fructose-1,6-diphosphate activation after 120 minutes incubation at low concentration at 37°C.