Regulation of Escherichia coli phosphofructokinase in situ

The activity of E. coli phosphofructokinase in situ has been studied in cells permeabilized to its substrates, products and effectors by a toluene-freezing treatment. The in situ enzyme exhibits moderate cooperativity in respect to F6P (n_H up to 2.0), rather low affinity for ATP (with Km up to 1 mM when saturated with F6P), activation by ADP, and inhibition, within the physiological range of concentrations, by high ATP and phosphoenolpyruvate. This behaviour of the enzyme in situ at concentrations of the effector metabolites as those reported in intact cells in glycolytic and gluconeogenic conditions could account for the changes of phosphofructokinase activity needed for metabolic regulation in vivo.