Kinetic and regulatory properties of pyruvate kinase isozymes from flight muscle and fat body of the cockroach, Periplaneta americana
Pyruvate kinases from flight muscle and fat body of the cockroach, Periplaneta americana, were purified to homogeneity. The two tissues contained different forms of the enzyme which were separable by starch gel electrophoresis and isoelectric focusing (pI=5.75 for flight muscle and 6.15 for fat body). Both enzymes had molecular weights of 235,000±20,000. Flight muscle pyruvate kinase displayed Michaelis-Menten kinetics with respect to both ADP and P-enolpyruvate with Km values of 0.27 and 0.04 mM, respectively. Km for Mg2+ was 0.60 mM and Ka for K+ was 15 mM. The enzyme was weakly inhibitied by four compounds, ATP, arginine-P, l-alanine and citrate with apparent Ki values of 3.5, 15, 20 and 24 mM, respectively. Competitive inhibition by 3 mM ATP or 10 mM arginine-P raised the Km for P-enolpyruvate to 0.067 or 0.057 mM. Fructose-1,6-P2 did not activate the enzyme but reversed inhibitions by ATP and arginine-P. Fat body pyruvate kinase showed sigmoidal kinetics with respect to P-enolpyruvate with S0.5=0.32 mM and nH=1.43. Km values for ADP and Mg2+ were 0.30 and 0.80 mM, respectively with a Ka for K+ of 10 mM. ATP and l-alanine were inhibitors of the enzyme; 2 mM ATP raised S0.5 for P-enolpyruvate to 0.48 mM while 3 mM l-alanine increased S0.5 to 0.84 mM. Neither citrate nor arginine-P inhibited the enzyme but citrate affected the enzyme by reversing l-alanine inhibition. Fat body pyruvate kinase was strongly activated by fructose-1,6-P2 with an apparent Ka of 1.5 M. Fructose-1,6-P2 at 0.1 mM reduced S0.5 for P-enolpyruvate to 0.05 mM and nH to 1.0. Flight muscle and fat body pyruvate kinases from the cockroach show properties analogous to those of the muscle and liver forms of mammalian pyruvate kinase. Fat body pyruvate kinase is suited for on-off function in a tissue with a gluconeogenic capacity. Strong allosteric control with a feed-forward activation by fructose-1,6-P2 is key to coordinating enzyme function with glycolytic rate. The function of flight muscle pyruvate kinase in energy production during flight is aided by a low Km for P-enolpyruvate, weak inhibitor effects by high energy phosphates and deinhibition of these effects by fructose-1,6-P2.
|Journal||Journal of Comparative Physiology B|
Storey, K. (1985). Kinetic and regulatory properties of pyruvate kinase isozymes from flight muscle and fat body of the cockroach, Periplaneta americana. Journal of Comparative Physiology B, 155(3), 339–345. doi:10.1007/BF00687476