title: Evidence for the presence of two conformations of the heme a3-Cu(B) pocket of cytochrome caa3 from Thermus thermophilus.
abstract: Resonance Raman (RR) and "light" minus "dark" Fourier transform infrared (FTIR) difference spectra are reported for the CO-bound caa(3) oxidase from Thermus thermophilus. Two Fe-CO stretching modes at 518 and 507 cm(-1), the Fe-C-O bending mode at 570 cm(-1), and three C-O modes of heme a(3) at 1958, 1967, and 1973 cm(-1) have been identified in the RR and FTIR spectra, respectively. The FTIR "light" minus "dark" spectrum indicates the formation of Cu(B)CO as revealed by its ν(CO) at 2060/2065 cm(-1). We assign the bands at 518 (ν(Fe-CO)) and 1967/1973 cm(-1) (ν(C-O)) as the α-conformation. We also assign the bands at 507 and 1958 cm(-1) (ν(C-O)) as originating from the β-conformation of the enzyme. A frequency upshift of the heme a(3) Fe-His mode is observed subsequent to CO photolysis from 209 cm(-1) in the equilibrium deoxy enzyme to 214 cm(-1) in the photoproduct. The caa(3) data, distinctly different from those of ba(3) oxidase, are discussed in terms of the coupling of the α- and β-conformations that occur in heme-copper oxidases with catalytic function. The dynamics between the heme a(3) and heme a propionates as revealed by the perturbation of the bending vibrations δ(prop) of hemes a and a(3) at 385 and 392 cm(-1), respectively, induced upon CO binding to heme a(3) is discussed in terms of the protonic connectivity between the heme a ring-D propionate/Arg site with that of the heme a(3) ring-D propionate-H(2)O site that leads to the highly conserved in the heme-copper oxidases water pool.
authors.affiliation: Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus.
authors.forename: Andrea
authors.initials: A
authors.lastname: Pavlou
authors.forename: Tewfik
authors.initials: T
authors.lastname: Soulimane
authors.forename: Eftychia
authors.initials: E
authors.lastname: Pinakoulaki
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry; D020134:Catalytic Domain; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry* / Q000378:metabolism; D045264:Cytochromes a / Q000737:chemistry* / Q000378:metabolism; D045266:Cytochromes a3 / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000031:analogs & derivatives* / Q000737:chemistry; D010782:Photolysis; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D016963:Thermus thermophilus / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D003574:Cytochrome c Group; D045266:Cytochromes a3; C435384:cytochrome caa(3); C027728:heme a; D006418:Heme; D003300:Copper; D002248:Carbon Monoxide; D045264:Cytochromes a