title: pH-dependent structural changes at the Heme-Copper binuclear center of cytochrome c oxidase.
abstract: The resonance Raman spectra of the aa3 cytochrome c oxidase from Rhodobacter sphaeroides reveal pH-dependent structural changes in the binuclear site at room temperature. The binuclear site, which is the catalytic center of the enzyme, possesses two conformations at neutral pH, assessed from their distinctly different Fe-CO stretching modes in the resonance Raman spectra of the CO complex of the fully reduced enzyme. The two conformations (alpha and beta) interconvert reversibly in the pH 6-9 range with a pKa of 7.4, consistent with Fourier transform infrared spectroscopy measurements done at cryogenic temperatures (D.M. Mitchell, J.P. Sapleigh, A.M.Archer, J.O. Alben, and R.B.Gennis, 1996, Biochemistry 35:9446-9450). It is postulated that the different structures result from a change in the position of the Cu(B) atom with respect to the CO due to the presence of one or more ionizable groups in the vicinity of the binuclear center. The conserved tyrosine residue (Tyr-288 in R. sphaeroides, Tyr-244 in the bovine enzyme) that is adjacent to the oxygen-binding pocket or one of the histidines that coordinate Cu(B) are possible candidates. The existence of an equilibrium between the two conformers at physiological pH and room temperature suggests that the conformers may be functionally involved in enzymatic activity.
authors.affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, New York, New York 10461, USA.
authors.forename: T K
authors.initials: TK
authors.lastname: Das
authors.forename: F L
authors.initials: FL
authors.lastname: Tomson
authors.forename: R B
authors.initials: RB
authors.lastname: Gennis
authors.forename: M
authors.initials: M
authors.lastname: Gordon
authors.forename: D L
authors.initials: DL
authors.lastname: Rousseau
mesh_terms: D000818:Animals; D001665:Binding Sites; D020134:Catalytic Domain; D002417:Cattle; D003300:Copper / Q000737:chemistry*; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000302:isolation & purification; D006418:Heme / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D011487:Protein Conformation; D012242:Rhodobacter sphaeroides / Q000201:enzymology; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013696:Temperature; D014443:Tyrosine / Q000737:chemistry
chemical_list: D014443:Tyrosine; D006418:Heme; D003300:Copper; D003576:Electron Transport Complex IV