Vacuolar H⁺-ATPase: An Essential Multitasking Enzyme in Physiology and Pathophysiology

Figure 2

Structure and subunit composition of V-ATPases. The model represents recent proposals regarding the subunit composition, stoichiometry, and organization of V-ATPases. A list of subunits with isoforms is provided. ATP hydrolysis occurs on the A-subunit and it is thought that the three subunits have at any specific time ATP, ADP-Pi, or ADP bound. The conformational changes in the AB heterohexagon promote turning of the central rotor and the ring of c and c′′ (b) subunits. The pathway of protons through the membranes includes both the rotating cb-ring and the a-subunit.