Received May 18, 2001
Structural arrangements and properties of redox components of the mitochondrial and bacterial proton-translocating NADH:quinone oxidoreductases are briefly described. A model for the mechanism of proton translocation at first coupling site, which emphasizes participation of specifically Complex I-associated ubisemiquinones, is discussed. An alternative mechanism is proposed where all redox reactions take place in a hydrophilic part of the enzyme and the free energy accumulated as conformational constraint drives the proton pump associated with the hydrophobic polypeptides.
KEY WORDS: NADH:quinone oxidoreductase, Complex I, respiratory chain, proton translocation, electrochemical coupling