Binding change model for ATP synthase

The nucleotide binding site (catalytic site) of the three dimers exists in three different conformations, termed loose (L), tight (T), and open (O).

The subunit rotates counterclockwise, driven by the passage of protons through channels in F0, while the dimer assemblies are held stationary by a stator.

Step 1 represents 120° rotation of the subunit, leading to a conformational change in all three dimers, such that the T site changes to an O site, leading to ATP release, and an O site changes to an L site, binding ADP and Pi.

The third site changes from an L conformation, with loosely bound ADP and Pi, to a T conformation, where the substrates are tightly bound, leading to ATP formation in step 2.