F-type ATP synthases have two large domains, a membrane integrated F_o part which is involved in proton transport and a hydrophilic F₁ part (subunits a₃b₃gde) which contains the ‘nucleotide’ (ATP, ADP), P_i, and Mg²⁺ binding sites. The nucleotide binding and dissociation steps at the three catalytic b-subunits of the F₁ part are coupled in the enzyme via long range conformational changes with proton binding, translocation and dissociation steps in the F_o part (subunits a, b₂ and c_10-12 for the E. coli enzyme).