Studies on the kinetic mechanism of oxidative phosphorylation

The kinetics of the synthesis of ATP from ADP and Pi by beef heart submitochondrial particles were examined. When Pi was the variable substrate positive cooperativity was observed, whereas if ADP was varied, linear double reciprocal plots were obtained. The analog of Pi, thiophosphate, was a noncompetitive inhibitor of ATP synthesis with respect to ADP, while the analog of ADP, AMP (CH2)P, was an uncompetitive Pi leads to ATP exchange inhibitor. The kinetics of the initial velocity isotopic exchanges of oxidative phosphorylation were also examined. When the Pi leads to ATP exchange was examined, it was found that if ADP concentration was held constant while ATP and Pi concentrations were varied at a constant ratio, linear double reciprocal plots were obtained. However, if Pi concentration was held constant and ADP and ATP concentrations were varied at constant ratio, apparent substrate inhibition was observed. The 2, 4-dinitrophenol-sensitive ADP leads to ATP exchange showed linear double reciprocal plots regardless of which components were varied. These results are interpreted to indicate that in the direction of ATP synthesis, the reaction is ordered, with Pi adding to the enzyme before ADP addition.