Phosphofructokinase from flight muscle of the cockroach, Periplaneta americana. Control of enzyme activation during flight
Phosphofructokinase (PFK) from the flight muscle of the cockroach, Periplaneta americana, was partially purified. Michaelis constants for ATP and Mg2+ were 0.05 ± 0.005 and 0.50 ± 0.038 mM while S0.5 for fructose-6-P was 16 ± 0.9 mM (h = 2.3 ± 0.4) at pH 7.0 and 9.4 ± 0.3 mM (h = 1.5 ± 0.3) at pH 8.0. ADP, fructose-1,6-P2 and citrate had no effect on cockroach PFK but ammonium ion, inorganic phosphate, AMP and fructose-2,6-P2 were all activators of enzyme activity with apparent Kas of 1.0 mM, 0.7 mM, 8.0 μM and 0.1 μM, respectively. Activators increased enzyme affinity for fructose-6-P and reduced enzyme substrate inhibition by high levels of ATP. Effects of activators were additive with strong synergistic interactions seen when AMP and fructose-2,6-P2 were added together; alone 0.16 mM AMP reduced S0.5 by 7-fold and 0.1 μM fructose-2,6-P2 reduced S0.5 by 1.7-fold but when added together S0.5 for fructose-6-P decreased by 114-fold to 0.14 mM. Addition of all four activators, at levels close to physiological concentrations in flight muscle (3 mM NH4 +, 10 mM Pi, 0.4 mM AMP and 1 μM fructose-2,6-P2), reduced S0.5 by 640-fold to 0.025 mM, a value within the physiological range of fructose-6-P concentrations in vivo. In combination all four activators also raised I50 for ATP to 18 mM compared to I50s of between 1.7 and 6.5 mM in the presence of each activator alone. At the initiation of flight full activation of PFK (allowing a maximal glycolytic rate) in flight muscle is accomplished through the combined effects of activators on PFK, in particular the effects of elevated concentrations of AMP and fructose-2,6-P2 in working muscle.
|Keywords||6-bisphosphate, activation of glycolysis, flight muscle metabolism, fructose-2, insect flight muscle, Periplaneta americana, Phosphofructokinase|
Storey, K. (1985). Phosphofructokinase from flight muscle of the cockroach, Periplaneta americana. Control of enzyme activation during flight. Insect Biochemistry, 15(5), 663–666. doi:10.1016/0020-1790(85)90130-1