Respiratory complex I

Respiratory complex I, or NADH:ubiquinone oxidoreductase, transfers electrons from NADH to ubiquinone and couples the process to proton translocation across the inner mitochondrial membrane. Its flavin and iron-sulfur centers form part of the electron-transfer pathway.

The resulting contribution to the proton gradient can support ATP synthesis. Electron transfer and proton movement are coupled molecular processes; the complex does not directly phosphorylate ADP. Its physiological direction and behavior depend on redox and membrane-potential conditions.