Proton translocation in the respiratory chain involving ubiquinone – a hypothetical semiquinone switch mechanism for complex I

Article type: Research Article

Authors: Brandt, Ulrich^;

Affiliations: Universitätsklinikum Frankfurt, Institut für Biochemie I, D‐60590 Frankfurt am Main, Germany

Note: [] Correspondence to: Universitätsklinkum Frankfurt, Institut für Biochemie I, ZBC, Theodor‐Stern‐Kai 7, Haus 25B, D‐60590 Frankfurt am Main, Germany. Tel.: +49 69 6301 6926; Fax: +49 69 6301 6970; E‐mail: brandt@ zbc.klinik.uni‐frankfurt.de.

Abstract: The protonmotive Q‐cycle is the generally accepted reaction scheme of the cytochrome bc_{1} complex of the respiratory chain. It employs the redox‐dependent protonation and deprotonation of ubiquinone (coenzyme Q_{10}) to translocate protons accross the inner mitochondrial or bacterial plasma membrane. The requirements for the operation of a similar mechanism in proton translocating NADH:ubiquinone oxidoreductase (complex I) and the specific roles of the ‘Rieske’ iron‐sulfur center in the cytochrome bc_{ 1} complex and iron‐sulfur center N‐2 in complex I are discussed. Recent results suggest that there is only one ubiquinone‐reactive site in complex I which seems to exclude a classical Q‐cycle type mechanism. Therefore, a “semiquinone switch” mechanism is proposed involving one tightly bound and one substrate quinone. It is based on the same principles as a Q‐cycle, but is a localized rather than a ligand conduction type mechanism.

Journal: Biofactors, vol. 9, no. 2-4, pp. 95-101, 1999