Editing Respiratory complex I (section)

=== Electron transfer mechanism ===
The proposed pathway for electron transport prior to ubiquinone reduction is as follows: NADH – FMN – N3 – N1b – N4 – N5 – N6a – N6b – N2 – Q, where Nx is a labelling convention for iron sulfur clusters.<ref name=":0">{{cite journal | vauthors = Sazanov LA | title = A giant molecular proton pump: structure and mechanism of respiratory complex I | journal = Nature Reviews. Molecular Cell Biology | volume = 16 | issue = 6 | pages = 375–88 | date = June 2015 | pmid = 25991374 | doi = 10.1038/nrm3997 | s2cid = 31633494 }}</ref> The high reduction potential of the N2 cluster and the relative proximity of the other clusters in the chain enable efficient electron transfer over long distance in the protein (with transfer rates from NADH to N2 iron-sulfur cluster of about 100 μs).<ref>{{cite journal | vauthors = Ohnishi T | title = Iron-sulfur clusters/semiquinones in complex I | journal = Biochimica et Biophysica Acta (BBA) - Bioenergetics | volume = 1364 | issue = 2 | pages = 186–206 | date = May 1998 | pmid = 9593887 | doi = 10.1016/s0005-2728(98)00027-9 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Bridges HR, Bill E, Hirst J | title = Mössbauer spectroscopy on respiratory complex I: the iron-sulfur cluster ensemble in the NADH-reduced enzyme is partially oxidized | journal = Biochemistry | volume = 51 | issue = 1 | pages = 149–58 | date = January 2012 | pmid = 22122402 | pmc = 3254188 | doi = 10.1021/bi201644x }}</ref>

The equilibrium dynamics of Complex I are primarily driven by the quinone redox cycle. In conditions of high proton motive force (and accordingly, a ubiquinol-concentrated pool), the enzyme runs in the reverse direction. Ubiquinol is oxidized to ubiquinone, and the resulting released protons reduce the proton motive force.<ref name="Efremov 1785–1795">{{cite journal | vauthors = Efremov RG, [[Leonid Sazanov|Sazanov LA]] | title = The coupling mechanism of respiratory complex I - a structural and evolutionary perspective | journal = Biochimica et Biophysica Acta (BBA) - Bioenergetics | volume = 1817 | issue = 10 | pages = 1785–95 | date = October 2012 | pmid = 22386882 | doi = 10.1016/j.bbabio.2012.02.015 | doi-access = free }}</ref>