Studies on Heart Phosphofructokinase

Crystalline sheep heart phosphofructokinase catalyzed the formation of ATP and fructose 6-phosphate from ADP and fructose 1,6-diphosphate (the reverse reaction). Optimal conditions for the reverse reaction were described and compared to those for the forward reaction. The rate of the reverse reaction was approximately 5% of the rate of the forward direction. Kinetic studies were carried out on the reverse reaction at pH 6.5 and pH 8.2. At an acidic pH, the saturation curve for fructose 1,6-di-P was sigmoidal and dependent upon the ADP concentration. At pH 8.2, the effect of one substrate on the Km of the second substrate was investigated. It appears that the slopes of double reciprocal plots remained constant and, therefore, both the Vmax and the Km values were altered. The results of several experiments indicate that the same molecular state of phosphofructokinase catalyzed both the forward and the reverse reactions.