Britain The Isotope - Exchange Reactions of Ox Heart

1. Ox heart phosphofructokinase catalyses isotope-exchange reactions at pH 6.7 between ADP and ATP, and between fructose 6-phosphate and fructose 1,6diphosphate, the latter reaction being absolutely dependent on the presence of the magnesium complex of ADP. 2. The reaction kinetics are hyperbolic with respect to substrate concentration for both exchange reactions (within the experimental error). 3. The influence of pH, AMP and citrate suggests that the fructose 6phosphate-fructose 1,6-diphosphate exchange is subject to effector control, and is abolished by dissociation ofthe enzyme. 4. These results are discussed in relation to the reaction mechanism of the enzyme.