FTIR spectroscopy shows weak symmetric hydrogen bonding of the QB carbonyl groups in Rhodobacter sphaeroides R26 reaction centres.
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.
Brudler
R
R
Lehrstuhl für Biophysik, Ruhr-Universität Bochum, Germany.
de Groot
H J
HJ
van Liemt
W B
WB
Gast
P
P
Hoff
A J
AJ
Lugtenburg
J
J
Gerwert
K
K
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
D002247:Carbon Isotopes; D045322:Photosynthetic Reaction Center Complex Proteins; D014451:Ubiquinone; C025204:Ubiquinone Q2