Photoreduction of the quinone pool in the bacterial photosynthetic membrane: identification of infrared marker bands for quinol formation.
The photoreduction of the quinone (Q) pool in the photosynthetic membrane of the purple bacterium Rhodobacter sphaeroides was investigated by steady-state and time-resolved Fourier transform infrared difference spectroscopy. The results are consistent with the existence of a homogeneous Q pool inside the chromatophore membrane, with a size of around 20 Q molecules per reaction center. IR marker bands for the quinone/quinol (Q/QH(2)) redox couple were recognized. QH(2) bands are identified at 1491, 1470, 1433 and 1388-1375 cm(-1). The 1491 cm(-1) band, which is sensitive to (1)H/(2)H exchange, is assigned to a C-C ring mode coupled to a C-OH mode. A feature at approximately 1743/1720 cm(-1) is tentatively related to a perturbation of the carbonyl modes of phospholipid head groups induced by QH(2) formation. Complex conformational changes of the protein in the amide I and II spectral ranges are also apparent during reduction and reoxidation of the Q pool.
Mezzetti
Alberto
A
Service de Bioénergétique, Bâtiment 532, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France.
Leibl
Winfried
W
Breton
Jacques
J
Nabedryk
Eliane
E
D020130:Bacterial Chromatophores / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D006873:Hydroquinones / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D011809:Quinones / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared
D006873:Hydroquinones; D045322:Photosynthetic Reaction Center Complex Proteins; D011809:Quinones