Figure 4.

Schematic of the complex I model by Gauthier et al. [72]. The seven-state proton pump is adapted from the six-state proton pump model of Magnus and Keizer [54,55]. The model includes proton pumping (5 → 6 → 1→ 2), NADH oxidation (2 → 3 → 4), ubiquinone reduction (4 → 7 → 5), and superoxide generation (4 → 2). Each cycle represents one electron transfer from NADH to ubiquinone or oxygen. The arrows represent the forward reaction direction, although all reactions are reversible. Reprinted/adapted with permission from Ref. [62].