FIGURE 3.

Model of electron transfer and proton translocation by complex I. The orientations of the membrane, Q-binding site, Fe-S center N2, and their interacting region in relation to the mechanical linkage to the three indirect proton pumps in the membrane domain are the same as Fig. 1. Oxidized redox centers are shown in green, those that have been reduced by a single electron are shown in red, and two electron reduction states are shown in blue. The transitions from state G to state H result in conformational changes in the N2-Q interacting region (represented by a purple box) that are coupled to the indirect movement of three protons in the membrane domain (as hypothesized in Ref. 13). See text for details.