Kinetic modelling of yeast phosphofructokinase.

Phosphofructokinase from baker's yeast (Saccharomyces cerevisiae) is an octameric enzyme which exhibits complex allosteric behaviour. In contrast to mammalian phosphofructokinase, the enzyme does not show association-dissociation behaviour. A systematic kinetic investigation at pH 7.2 in dependence on the substrates, fructose 6-phosphate and ATP as well as on the effectors AMP and ADP is presented. The results are interpreted in terms of a structure oriented theoretical model. Because the two state model of Monod, Wyman and Changeux proved to be insufficient for interpretation of the experimental data, it was extended to a four state model in which the basic conformations R and T of the enzyme are split into subconformations R1 and R2 as well as T1 and T2, respectively. It is assumed that fructose 6-phosphate and the adenine nucleotides influence different allosteric equilibria. The model permits a precise quantitative description of the experimental data.