Interconvertible forms of phosphofructokinase of rabbit liver

Abstract

Rabbit liver phosphofructokinase prepared and stored as described herein exhibits classical Michaelis Menten kinetics and gives a hyperbolic curve when rates at different fructose 6-phosphate (F-6-P) concentrations were determined by adding enzyme last. It gives a sigmoidal curve when the rates were determined after prior dilution of the stock enzyme and adding F-6-P last. These results suggest that the enzyme may exist in interconvertible forms, differing widely in their apparent K m values for F-6-P and that F-6-P and other positive effectors transform the enzyme into form(s) which has low apparent K m value for F-6-P.