ATP Synthase Mechanism

Step 1

A single proton from the inner mitochondrial membrane space (cytosol) enters the ATP synthase complex via the F0, alpha subunit, hydrophilic, cytoplasmic half-channel

Step 2

The proton in the F0, alpha subunit, hydrophilic, cytoplasmic half-channel protonates Asp 61 on one of the c-subunits of the c-subunit ring

Step 3

With the Asp 61 charge now neutralized, the uncharged Asp 61 can be exposed to the hydrophobic interior of the inner mitochondrial membrane when the c-subunit ring rotates. The c-subunit ring rotates to allow the next c-subunit to be protonated by a proton entering the F0, alpha subunit, hydrophilic, cytoplasmic half-channel

Step 4

Eventually, all of the c-subunits of the c-subunit ring become protonated (uncharged). When these rotate back to the F0 a-subunit, the Asp 61 becomes de-protonated, releasing the proton to the mitochondrial matrix via the other a-subunit, hydrophilic, matrix half-channel

Step 5

Since the c-subunit ring is connected to the gamma-subunit, the gamma-subunit core rotates (spins) within the alpha3beta3 hexamer for the F1 subunit

Step 7

the gamma-subunit core has 3 different, interactive surfaces (or “faces”) that convert the beta-subunits in the alpha3beta3 hexamer to adopt 1 of 3 different conformations 

The three beta conformations

O

L
T

O-conformation

ATP just generated is released and new ADP and Pi enter the active site of the beta subunit

L-conformation

ADP and Pi are “loosely” bound to the beta-subunit

T-conformation

ADP and Pi are tightly bound to the beta subunit and ADP and Pi are converted into ATP