Photoreduction of the quinone pool in the bacterial photosynthetic membrane: identification of infrared marker bands for quinol formation

• Published in: FEBS letters 2003-02, Vol.537 (1-3), p.161-165
• Main Authors: Mezzetti, Alberto, Leibl, Winfried, Breton, Jacques, Nabedryk, Eliane
• Format: Article
• Language: English
• Subjects: 2,3-dimethoxy-5-methyl-6-polypropenyl-1,4-benzoquinone; Bacterial Chromatophores - metabolism; Cell Membrane - metabolism; Fourier transform infrared; FTIR; Hydroquinones - metabolism; Intracellular Membranes - metabolism; Kinetics; Oxidation-Reduction; Photosynthetic membrane; Photosynthetic Reaction Center Complex Proteins - chemistry; Photosynthetic Reaction Center Complex Proteins - metabolism; primary and secondary quinone electron acceptors, respectively; primary electron donor; QA and QB; QH2; Quinol; quinone; Quinone pool; Quinones - metabolism; reaction center; Rhodobacter sphaeroides - metabolism; Spectroscopy, Fourier Transform Infrared
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/S0014-5793(03)00118-2

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/QH2) redox couple were recognized. QH2 bands are identified at 1491, 1470, 1433 and 1388–1375 cm−1. The 1491 cm−1 band, which is sensitive to 1H/2H exchange, is assigned to a C–C ring mode coupled to a C–OH mode. A feature at ∼1743/1720 cm−1 is tentatively related to a perturbation of the carbonyl modes of phospholipid head groups induced by QH2 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.