title: Spectroscopic and electrochemical studies on active-site transitions of the type 1 copper protein pseudoazurin from Achromobacter cycloclastes.
abstract: The single type 1 copper protein pseudoazurin from Achromobacter cycloclastes gives reversible electrochemical behavior at a (4-pyridyl)disulfide-modified gold electrode. Measurements carried out at 25.0 degrees C indicate a midpoint reduction potential of E 1/2 = 260 mV versus normal hydrogen electrode at pH 7.0 and a peak-to-peak separation of delta Ep = 59 mV. The diffusion coefficient and heterogeneous electron transfer rate constant are estimated to be 2.23 x 10(-6) cm2 s-1 and 3.7 x 10(-2) cm s-1, respectively. Also, controlled potential electrolysis indicates a 1-electron transfer process and a formal reduction potential of 259 mV versus normal hydrogen electrode for the Cu(II)/Cu(I) couple. The heterogeneous electron transfer rate constant determined at the (4-pyridyl)disulfide-modified gold electrode at pH 4.6 is 6.7 x 10(-3) cm s-1, consistent with a slower process at the positively charged electrode surface. At pH 11.3, UV-visible, EPR, and resonance Raman spectra indicate a conversion of the distorted tetrahedral copper geometry to a trigonal structure. The trigonal form has elongated axial bonding and an axial EPR spectrum. At pH 11.3, the reduction potential is further decreased, and Cu-S bands in resonance Raman spectra at 330-460 cm-1 are shifted to higher energy (approximately 10 cm-1), consistent with a stronger Cu-S bond.
authors.affiliation: Department of Chemistry, Ibaraki University, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kohzuma
authors.forename: C
authors.initials: C
authors.lastname: Dennison
authors.forename: W
authors.initials: W
authors.lastname: McFarlane
authors.forename: S
authors.initials: S
authors.lastname: Nakashima
authors.forename: T
authors.initials: T
authors.lastname: Kitagawa
authors.forename: T
authors.initials: T
authors.lastname: Inoue
authors.forename: Y
authors.initials: Y
authors.lastname: Kai
authors.forename: N
authors.initials: N
authors.lastname: Nishio
authors.forename: S
authors.initials: S
authors.lastname: Shidara
authors.forename: S
authors.initials: S
authors.lastname: Suzuki
mesh_terms: D000421:Alcaligenes / Q000737:chemistry*; D001400:Azurin / Q000031:analogs & derivatives* / Q000737:chemistry; D001665:Binding Sites; D003300:Copper; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D008667:Metalloproteins / Q000737:chemistry*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011199:Potentiometry; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman
chemical_list: D008667:Metalloproteins; C047163:pseudoazurin; D001400:Azurin; D003300:Copper