title: The cytochrome subunit structure in the photosynthetic reaction center of Chromatium minutissimum.
abstract: Gel-electrophoretic assay revealed that the photosynthetic reaction center (RC) of Chromatium minutissimum, in contrast to the well-known RC Rhodopseudomonas viridis, consists of five rather than four subunits with molecular masses of 37, 34, 25, 19, and 17 kDa. The 37- and 19-kDa subunits are stained with tetramethylbenzidine for the cytochrome c hemes. Absorption spectra show that the concentration of reduced cytochromes in the C. minutissimum RC poised at redox potential of -150 mV (fully reduced pool of hemes) is about three times more than in the C. minutissimum RC poised at redox potential of +260 mV (only high-potential hemes are reduced). The results of redox titration of absorption changes at the cytochrome c alpha-band are most appropriately approximated by a six-component theoretical curve with the midpoint potentials of Em1 = 390 mV, Em2 = 320 mV, Em3 = 210 mV, Em4 = 100 mV, Em5 = 20 mV, and Em6 = -50 mV. Possible functions of the cytochromes with the midpoint potentials 210 and 100 mV, which have not been found in purple bacteria before, are discussed.
authors.affiliation: Department of Biophysics, Biological Faculty, Lomonosov State University, Moscow, Russia.
authors.forename: S K
authors.initials: SK
authors.lastname: Chamorovsky
authors.forename: N I
authors.initials: NI
authors.lastname: Zakharova
authors.forename: S M
authors.initials: SM
authors.lastname: Remennikov
authors.forename: Y a
authors.initials: Ya
authors.lastname: Sabo
authors.forename: A B
authors.initials: AB
authors.lastname: Rubin
mesh_terms: D002844:Chromatium / Q000737:chemistry* / Q000254:growth & development; D003574:Cytochrome c Group / Q000032:analysis / Q000737:chemistry*; D006418:Heme / Q000032:analysis; D046911:Macromolecular Substances; D008970:Molecular Weight; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000302:isolation & purification; D013053:Spectrophotometry
chemical_list: D003574:Cytochrome c Group; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins; D006418:Heme