Some properties of phosphofructokinase from kidney cortex and their relation to glucose metabolism.

1. Phosphofructokinase from rat kidney cortex has been partially purified by using a combination of isoelectric and ammonium sulphate precipitation. This preparation was free of enzymes which interfered with the measurement of either product of phosphofructokinase. 2. At concentrations greater than the optimum, ATP caused inhibition which was decreased by raising the fructose 6-phosphate concentration. This suggested that ATP reduced the affinity of phosphofructokinase for the other substrate. Citrate potentiated the ATP inhibition. 3. AMP and fructose 1,6-diphosphate relieved the inhibition by ATP or citrate by increasing the affinity of the enzyme for fructose 6-phosphate. 4. K(+) is shown to stimulate and Ca(2+) to inhibit phosphofructokinase. 5. The similarity between the complex properties of phosphofructokinase from kidney cortex and other tissues (e.g. cardiac and skeletal muscle, brain and liver) suggests that the enzyme in kidney cortex tissue is normally subject to metabolic control, similar to that in other tissues.