title: Redox-linked transient deprotonation at the binuclear site in the aa(3)-type quinol oxidase from Acidianus ambivalens: implications for proton translocation.
abstract: The hyperthermophilic archaeon Acidianus ambivalens expresses a membrane-bound aa(3)-type quinol oxidase, when grown aerobically, that we have studied by resonance Raman spectroscopy. The purified aa(3) oxidase, which does not contain bound quinol, undergoes a reversible slow conformational change at heme a(3) upon reduction, as indicated by a change in the frequency of its heme formyl stretching mode, from 1,660 cm(-1) to 1,667 cm(-1). In contrast, upon reduction of the integral membrane enzyme or the purified enzyme preincubated with decylubiquinol, this mode appears at 1,667 cm(-1) much more rapidly, suggesting a role of the bound quinol in controlling the redox-linked conformational changes. The shift of the formyl mode to higher frequency is attributed to a loss of hydrogen bonding that is associated with a group having a pKa of approximately 3.8. Based on these observations, a crucial element for proton translocation involving a redox-linked conformational change near the heme a(3) formyl group is postulated.
authors.affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
authors.forename: T K
authors.initials: TK
authors.lastname: Das
authors.forename: C M
authors.initials: CM
authors.lastname: Gomes
authors.forename: M
authors.initials: M
authors.lastname: Teixeira
authors.forename: D L
authors.initials: DL
authors.lastname: Rousseau
mesh_terms: D003576:Electron Transport Complex IV / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006860:Hydrogen Bonding; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D011487:Protein Conformation; D011522:Protons; D011809:Quinones / Q000378:metabolism; D013059:Spectrum Analysis, Raman; D013329:Structure-Activity Relationship; D016944:Sulfolobus / Q000201:enzymology*
chemical_list: D011522:Protons; D011809:Quinones; D006418:Heme; D010088:Oxidoreductases; C020094:duroquinol oxidase; D003576:Electron Transport Complex IV