Computer modeling of muscle phosphofructokinase kinetics

The kinetics of the phosphofructokinase reaction were studied by computer modeling. A general random order, two-state allosteric model, of which the Monod-Wyman-Changeux model is a limiting case, was found to most accurately reproduce the experimental observations of Pettigrew & Frieden (1979a,b). A simplified model with Hill coefficients was found to fit almost as well. In these models substrates bind preferentially to and stabilize the enzyme in the R state, and ATPH3− the inhibitory species, binds preferentially to and stabilizes the enzyme in the T state. Enzymatic activity is regulated by conversion from the R to the T state, which is effected by protonation, especially of the uncomplexed enzyme, but the experimental data are inadequate for accurate estimation of the pKa, of the enzyme. Random order binding of substrates is an important cause of sigmoidal kineticS Additional experiments that would aid in the discrimination among rival models are described.