Changes in the modulations of kinetics and allosteric properties of muscle phosphofructokinase of young and old rats.

In vitro studies on various modulations in kinetics and allosteric properties of muscle phosphofructokinase (EC 2.7.1.11) were undertaken, using purified enzyme from young (25-weeks) and old (100-weeks) albino rats. In comparison to normal K0.5 values for fructose-6-phosphate, increase in this value in response to ATP and citrate inhibition, decrease in K0.5 due to AMP activation and extent of ATP inhibition with increase in pH, were observed to be decreased more markedly with the enzyme of old than with that of young rats. Extent of citrate inhibition, reversals of ATP and citrate effects in response to AMP activation, and synergism of citrate and ATP inhibitions were also seen to be decreased considerably with muscle PFK of old in comparison to that of young rats. Such age-related changes in muscle PFK suggest the alterations in allosteric regulation of this enzyme during aging of the animal.