Activated Q-cycle as a common mechanism for cytochrome bc(1) and cytochrome b(6)f complexes

Autor(en): Mulkidjanian, Armen Y.
Stichwörter: Biochemistry & Molecular Biology; Biophysics; Cytochrome b; Electron transfer; FLASH-INDUCED TURNOVER; IRON-SULFUR PROTEIN; OXYGENIC PHOTOSYNTHESIS; Photosynthesis; PHOTOSYNTHETIC ELECTRON-TRANSFER; Plastoquinone; Proton transfer; PROTON TRANSLOCATION; QUINOL OXIDATION SITE; RESPIRATORY-CHAIN; Rhodobacter capsulatus; Rhodobacter sphaeroides; RHODOBACTER-CAPSULATUS; RHODOPSEUDOMONAS-SPHAEROIDES; Ubiquinol cytochrome c oxidoreductase; UBIQUINOL OXIDATION; Ubiquinone
Erscheinungsdatum: 2010
Herausgeber: ELSEVIER
Journal: BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volumen: 1797
Ausgabe: 12, SI
Startseite: 1858
Seitenende: 1868
Zusammenfassung: 
Cytochrome bc(1) complexes of animals and bacteria ( hereafter bc(1)) as well as related cytochrome b(6)f complexes of plants and cyanobacteria (hereafter bf) are dimeric quinol cytochrome c/plastocyanin oxidoreductases capable of translocating protons across energy-converting membranes The commonly accepted Q-cycle mechanism suggests that these enzymes oxidize two quinol molecules in their catalytic centers P to yield one quinol molecule in another catalytic center N Earlier based upon data on flash-induced redox changes of cytochromes b and c(1) voltage generation and proton transfer in membrane vesicles of Rhodobacter capsulatus we have put forward a scheme of an ``activated Q-cycle'' for the bc(1) The scheme suggests that the bc(1) dimers being ``activated'' by injection of electrons from the membrane ubiquinol pool via centers N steadily contain two electrons in their cytochrome b moieties under physiological conditions most likely as a bound semiquinone in center N of one monomer and a reduced high-potential heme b in the other monomer Then the oxidation of each ubiquinol molecule in centers P of an activated bc(1) should result in a complete catalytic cycle leading to the formation of a ubiquinole molecule in the one of enzyme s centers N and to voltage generation Here It is argued that a similar pre-loading by two electrons can explain the available data on flash-induced reactions in cytochrome b(6)f-complexes of green plants and cyanobacteria (C) 2010 Elsevier B V All rights reserved
ISSN: 00052728
DOI: 10.1016/j.bbabio.2010.07.008

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