title: Characterization of the reaction center bound tetraheme cytochrome of Rhodocyclus tenuis.
abstract: Properties of the tetrahemic reaction center bound cytochrome have been investigated by different techniques. The mid-point potentials of the four hemes were determined by redox titration. The best fit of the data was obtained with a (n = 1) Nernst curve by using the following values of the redox parameters: Em = +420 mV for the two high-potential hemes and Em = +110 and +60 mV for the two low-potential hemes. The mid-point potentials of the two high-potential hemes are the highest reported so far. The spectral properties of the four hemes in the alpha-band have been determined by absorption spectroscopy and measurements of light-induced difference spectra in membranes of Rhodocyclus tenuis. The two high potential hemes present very similar spectra centered at 557 nm. The absorption spectra of the two low-potential hemes are very similar, and their alpha-band centered around 551 nm. Spectral properties at 100 K and the linear dichroism of optical transitions allow the determination of the relative orientations of the hemes with respect to the membrane plane. The orientation patterns thus obtained corresponds to none of the arrangements described so far for reaction center bound cytochromes.
authors.affiliation: C.E.A., DEVM-LBC, C.E.A. Cadarache, Saint-Paul-lez-Durance, France.
authors.forename: L
authors.initials: L
authors.lastname: Menin
authors.forename: B
authors.initials: B
authors.lastname: Schoepp
authors.forename: D
authors.initials: D
authors.lastname: Garcia
authors.forename: P
authors.initials: P
authors.lastname: Parot
authors.forename: A
authors.initials: A
authors.lastname: Verméglio
mesh_terms: D001426:Bacterial Proteins; D002942:Circular Dichroism; D003574:Cytochrome c Group / Q000737:chemistry / Q000378:metabolism; D003580:Cytochromes / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D012245:Rhodospirillales / Q000201:enzymology*; D013053:Spectrophotometry; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D003574:Cytochrome c Group; D003580:Cytochromes; D007506:Iron-Sulfur Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D006418:Heme; C017167:cytochrome C(551)