title: FTIR spectroscopy shows weak symmetric hydrogen bonding of the QB carbonyl groups in Rhodobacter sphaeroides R26 reaction centres.
abstract: The absorption frequencies of the C = O and C = C (neutral state) and of the C...O (semiquinone state) stretching vibrations of QB have been assigned by FTIR spectroscopy, using native and site-specifically 1-, 2-, 3- and 4-13C-labelled ubiquinone-10 (UQ10) reconstituted at the QB binding site of Rhodobacter sphaeroides R26 reaction centres. Besides the main C = O band at 1641 cm-1, two smaller bands are observed at 1664 and 1651 cm-1. The smaller bands at 1664 and 1651 cm-1 agree in frequencies with the 1- and 4-C = O vibrations of unbound UQ10, showing that a minor fraction is loosely and symmetrically bound to the protein. The larger band at 1641 cm-1 indicates symmetric H-bonding of the 1- and 4-C = O groups for the larger fraction of UQ10 but much weaker interaction as for the 4-C = O group of QA. The FTIR experiments show that different C = O protein interactions contribute to the factors determining the different functions of UQ10 at the QA and the QB binding sites.
authors.affiliation: Lehrstuhl für Biophysik, Ruhr-Universität Bochum, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Brudler
authors.forename: H J
authors.initials: HJ
authors.lastname: de Groot
authors.forename: W B
authors.initials: WB
authors.lastname: van Liemt
authors.forename: P
authors.initials: P
authors.lastname: Gast
authors.forename: A J
authors.initials: AJ
authors.lastname: Hoff
authors.forename: J
authors.initials: J
authors.lastname: Lugtenburg
authors.forename: K
authors.initials: K
authors.lastname: Gerwert
mesh_terms: D001665:Binding Sites; D002247:Carbon Isotopes; D006860:Hydrogen Bonding; D007700:Kinetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared; D014451:Ubiquinone / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D045322:Photosynthetic Reaction Center Complex Proteins; D014451:Ubiquinone; C025204:Ubiquinone Q2