Activation of rat erythrocyte phosphofructokinase by AMP and by non-physiological concentrations of cyclic AMP.

Cyclic AMP (300 micron) activates phosphofructokinase from dialyzed haemolysates of mature rat erythrocytes. The main conclusions are: a) Cyclic AMP, at pH 7.1 and low concentrations of fructose-6-phosphate, is able to reverse the inhibition produced by different amounts of ATP (up to 1.5 mM). b) The cyclic nucleotide is a positive allosteric effector of the enzyme as shown by the displacement of sigmoidal fructose-6-phosphate saturation curve to hyperbolic kinetics in the presence of inhibitory concentrations (1.5 mM) of ATP.c) Cyclic AMP has no significant influence as deinhibitor of phosphofructokinase either at pH 7.1 and non-inhibitory levels (0.25 mM) of ATP or at pH 8.1 and inhibitory (1.5 mM) or non-inhibitory (0.25 mM) concentrations of ATP. Similar conclusions were obtained with 300 micron AMP but not at a lower concentration (3 micron) with both nucleotides. The comparison of cyclic AMP result with those obtained under similar concentrations of AMP suggest that cyclic AMP is really only an "in vitro" modulator of the enzyme from rat erythrocytes, presumably at an AMP regulatory stie, since non-physiological concentrations are required to act as deinhibitor.