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ATP Synthesis:-The Proton Gradient Drives the Release of ATP from the Enzyme Surface

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  709

2026-06-21

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ATP Synthesis:-The Proton Gradient Drives the Release of ATP from the Enzyme Surface

Although ATP synthase equilibrates ATP with ADP+P_i, in the absence of a proton gradient the newly synthesized ATP does not leave the surface of the enzyme.

It is the proton gradient that causes the enzyme to re lease the ATP formed on its surface. The reaction coordinate diagram of the process (Fig. 19–22) illustrates the difference between the mechanism of ATP synthase and that of many other enzymes that catalyze endergonic reactions. For the continued synthesis of ATP, the enzyme must cycle between a form that binds ATP very tightly and a form that releases ATP. Chemical and crystallo graphic studies of the ATP synthase have revealed the structural basis for this alternation in function.

FIGURE 19–22 Reaction coordinate diagrams for ATP synthase and for a more typical enzyme. In a typical enzyme-catalyzed reaction (left), reaching the transition state (‡) between substrate and product is the major energy barrier to overcome. In the reaction catalyzed by ATP synthase (right), release of ATP from the enzyme, not formation of ATP, is the major energy barrier. The free-energy change for the formation of ATP from ADP and Pi in aqueous solution is large and positive, but on the enzyme surface, the very tight binding of ATP provides sufficient binding energy to bring the free energy of the enzyme-bound ATP close to that of ADP+Pi, so the reaction is readily reversible. The equilibrium constant is near 1. The free energy required for the release of ATP is provided by the proton-motive force.