Abstract
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.
Highlights
The kinetics of the synthesis of ATP from ADP and P, by beef heart submitochondrial particles were examined
The catalytic mechanism of ATP synthesis could most be viewed as the binding of ADP and Pi to form the basic components of the central complex of enzyme and transition state intermediates
To examine the kinetic parameters governing this process, both ADP and Pi were used as variable substrates in initial velocity and isotopic exchange studies of ATP synthesis, catalyzed by beef heart submitochondrial particles
Summary
Some kinetic properties of the H,O + P, exchange reaction have been explored with submitochondrial particles prepared either by sonication [15] or by digitonin treatment [16] One of these studies [16] directly addresses the question of a mandatory binding order for ADP and P, during ATP synthesis, and in this case no definite conclusion was reached. Workers in this field have depicted ATP synthesis as occurring with either ADP [17] or P, [18] combining with the enzyme as the first substrate. A preliminary report of our conclusions has been published [19]
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