title: Kinetic properties of rat liver pyruvate kinase at cellular concentrations of enzyme, substrates and modifiers.
abstract: Kinetic properties of rat liver pyruvate kinase type I at pH7.5 and 6.5 were studied with physiological ranges of substrates, modifiers and Mg(2+) concentrations at increasing enzyme concentrations, including the estimated cellular concentrations (approx. 0.1mg/ml). Enzyme properties appear unaffected by increased enzyme concentration if phosphoenolpyruvate, fructose 1,6-diphosphate and inhibitors are incubated with enzyme before starting the reaction with ADP. Our data suggest that minimum cellular concentrations of MgATP and l-alanine provide virtually complete inhibition of pyruvate kinase I at pH7.5. The most likely cellular control of existing pyruvate kinase I results from the strong restoration of enzyme activity by the small physiological amounts of fructose 1,6-diphosphate. Decreasing the pH to 6.5 also restores pyruvate kinase activity, but to only about one-third of its activity in the presence of fructose 1,6-diphosphate. Neither pyruvate nor 2-phosphoglycerate at cellular concentrations inhibit the enzyme significantly.
mesh_terms: D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000409:Alanine / Q000494:pharmacology; D000818:Animals; D002848:Chromatography, DEAE-Cellulose; D005636:Fructosephosphates; D005994:Glycerophosphates; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008274:Magnesium / Q000494:pharmacology; D010728:Phosphoenolpyruvate; D011770:Pyruvate Kinase / Q000037:antagonists & inhibitors; D011773:Pyruvates; D051381:Rats
chemical_list: D005636:Fructosephosphates; D005994:Glycerophosphates; D011773:Pyruvates; D000244:Adenosine Diphosphate; D010728:Phosphoenolpyruvate; D000255:Adenosine Triphosphate; D011770:Pyruvate Kinase; D008274:Magnesium; D000409:Alanine