Figure 16-30. The binding-change mechanism of ATP synthesis from ADP and Pi by the F0F1 complex.

Figure 16-30The binding-change mechanism of ATP synthesis from ADP and Pi by the F0F1 complex

This view is looking up at F1 from the membrane surface (see Figure 16-28). The three β subunits alternate between three conformational states that differ in their binding affinities for ATP, ADP, and Pi. Step  1 : After ADP and Pi bind to one of the three β subunits (here, arbitrarily designated β1) whose nucleotide-binding site is in the O (open) conformation, proton flux powers a 120° rotation of the γ subunit (relative to the fixed β subunits). The causes an increase in the binding affinity of the β1 subunit for ADP and Pi to L (low), an increase in the binding affinity of the β3 subunit for ADP and Pi from L to T (tight), and a decrease in the binding affinity of the β2 subunit for ATP from T to O, causing release of the bound ATP. Step  2 : The ADP and Pi in the T site (here the β3 subunit) form ATP, a reaction that does not require an input of energy, and ADP and Pi bind to the β2 subunit, which is in the O state. This generates an F1 complex identical with that which started the process (upper left) except that it is rotated 120°. Step  1 now occurs again, and the cycling of the O → L → T → O conformations of each β subunit continues. [Adapted from P. Boyer, 1989, FASEB J. 3:2164, and Y. Zhou et al., 1997, Proc. Nat’l. Acad. Sci. USA 94:10583.]

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ATP Synthesis

From: Section 16.2, Electron Transport and Oxidative Phosphorylation

Cover of Molecular Cell Biology
Molecular Cell Biology. 4th edition.
Lodish H, Berk A, Zipursky SL, et al.
New York: W. H. Freeman; 2000.
Copyright © 2000, W. H. Freeman and Company.

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