title: Fixing the Q cycle.
abstract: Mitchell's key insight that all bioenergetic membranes run on the conversion of redox energy into transmembrane electrical and proton gradients took the form 30 years ago of a working model of the Q cycle of cytochrome bc1, which operates reversibly on coupled electron and proton transfers of quinone at two binding sites on opposite membrane faces. His remarkable model still stands today, but he had no structural information to provide understanding into how dangerous short-circuit redox reactions were avoided. Now, it is clear that the Q cycle must be fixed with a special mechanism that avoids semiquinone-mediated short circuits. Either the redox states of the quinone electron-transfer partners double-gate the semiquinone-intermediate stability, or semiquinone is avoided altogether in concerted double-electron transfer.
authors.affiliation: The Johnson Research Foundation, Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Artur
authors.initials: A
authors.lastname: Osyczka
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Moser
authors.forename: P Leslie
authors.initials: PL
authors.lastname: Dutton
mesh_terms: D004579:Electron Transport / Q000502:physiology*; D014450:Electron Transport Complex III / Q000737:chemistry / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011522:Protons; D011809:Quinones / Q000737:chemistry
chemical_list: D011522:Protons; D011809:Quinones; D014450:Electron Transport Complex III