title: Absence of large-scale displacement of quinone QB in bacterial photosynthetic reaction centers.
abstract: Photosynthesis transforms light into chemical energy by coupling electron transfer to proton uptake at the quinone Q(B). The possibility of initiating this process with a brief pulse of light and the known X-ray structure makes the photosynthetic bacterial reaction center a paradigm for studying coupled electron-proton transfer in biology. It has been established that electron transfer from the primary quinone Q(A) to Q(B) is gated by a protein conformational change. On the basis of a dramatic difference in the location of Q(B) in structures derived from crystals cooled to 90 K either under illumination or in the dark, a functional model for the gating mechanism was proposed whereby neutral Q(B) moves 4.5 A before receiving the electron from Q(A)(-) [Stowell, M. H. B., McPhillips, T. M., Rees, D. C., Soltis, S. M., Abresch, E., and Feher, G. (1997) Science 276, 812-816]. Isotope-edited FTIR difference spectroscopy of Q(B) photoreduction at 290 and 85 K is used to investigate whether Q(B) moves upon reduction. We show that the specific interactions of the carbonyl groups of Q(B) and Q(B)(-) with the protein at a single binding site remain identical at both temperatures. Therefore, the different locations of Q(B) reported in many X-ray crystal structures probably are unrelated to functional electron transfer from Q(A)(-) to Q(B).
authors.affiliation: Service de Bioénergétique, Bât. 532, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France. cadara3@dsvidf.cea.fr
authors.forename: Jacques
authors.initials: J
authors.lastname: Breton
mesh_terms: D016227:Benzoquinones / Q000737:chemistry*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004579:Electron Transport; D005615:Freezing; D006860:Hydrogen Bonding; D008027:Light; D010084:Oxidation-Reduction; D010782:Photolysis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D012242:Rhodobacter sphaeroides / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D014451:Ubiquinone / Q000737:chemistry
chemical_list: D016227:Benzoquinones; D045322:Photosynthetic Reaction Center Complex Proteins; D014451:Ubiquinone; C004532:quinone