Respiratory Complex I: Structure, redox components, and possible mechanisms of energy transduction

Structural arrangements and properties of redox components of the mitochond rial and bacterial proton-translocating NADH:quinone oxidoreductases are br iefly described. A model for the mechanism of proton translocation at first coupling site, which emphasizes participation of specifically Complex 1-as sociated ubisemiquinones, is discussed, Ail alternative mechanism is propos ed where all redox reactions take place in a hydrophilic part of the enzyme and the free energy accumulated as conformational constraint drives the pr oton pump associated with the hydrophobic polypeptides.