A phosphofructokinase mutant of Escherichia coli altered in its allosteric properties impairs gluconeogenic growth.

The regulation of metabolic fluxes is accomplished by modulation of key enzyme catalyzed reactions. This modulation takes place partially through the control of the catalytic activity of enzymes labelled as regulatory enzymes. The kinetic behavior of many regulatory enzymes can be explained in terms of multiple binding sites for effector molecules. Of these, the ones that play their control over catalysis by binding at an allosteric site have been considered of much importance. Nevertheless, proof that the effects observed in vitro, are in fact responsible for the physiological regulation in vivo, is scarce. In this regard, mutant enzymes altered in their allosteric properties might be useful. This will be illustrated with an enzyme considered crucial for the regulation of carbohydrate metabolism, namely phosphofructokinase. We present here the comparison of some of the kinetic and structural properties of wild type phosphofructokinase-2 of E. coli and of a mutant form which impairs gluconeogenic growth, an indication of the significance of the in vivo regulation. The main differences between the enzymes are their kinetic reaction mechanism, inhibitability by ATP, and aggregation states in the presence of substrates and effectors. So far these differences support only speculations as to the mechanism of the gluconeogenic impairment observed in strains that contain the mutant enzyme, a few of which are offered.