PROBING THE SECONDARY QUINONE (QB) ENVIRONMENT IN PHOTOSYNTHETIC BACTERIAL REACTION CENTERS BY LIGHT-INDUCED FTIR DIFFERENCE SPECTROSCOPY

The photoreduction of the secondary electron acceptor, Q(B), has been characterized by light-induced Fourier transform infrared difference spectroscopy of Rb. sphaeroides and Rp. viridis reaction centers. The reaction centers were supplemented with ubiquinone (UQ10 or UQ0). The Q(B)-state was generated either by continuous illumination at very low intensity or by single flash in the presence of redox compounds which rapidly reduce the photooxidized primary electron donor P+. This approach yields spectra free from P and P+ contributions making possible the study of the microenvironment of Q(B) and Q(B)-. Assignments are proposed for the C...O vibration of Q(B)- and tentatively for the C = O and C = C vibrations of Q(B).