Magnetic interaction between Q(A)(-center dot) and the triplet state of the primary donor in modified reaction centers of the photosynthetic bacterium Rhodobacter sphaeroides R26

摘要

The interaction between the reduced primary acceptor quinone (Q(A)-.), and the triplet state of the primary donor 3D is investigated with time-resolved continuous-wave EPR. The trough at high-field in the Q(A)-. electron-spin polarized X-band EPR-spectrum at early delay times after the laser flash [De Groot et al. (1985) Biochim. Biophys. Acta 808, 13-20] is studied as a function of temperature and of the delay, in zinc-reconstituted reaction centers, with and without carotenoid. In all cases investigated a decrease in 3D concentration is accompanied by a simultaneous attenuation of the high-field trough in the Q(A)-. EPR spectrum. These observations confirm the hypothesis that the line-shape of Q(A)-. at short delay times is influenced by a magnetic interaction with 3D. The line-shape of the Q(A)-. electron-spin polarized EPR spectrum directly after the laser flash, could be very well simulated using an extension of the model of Here et al. [Hore, P.J. et al. (1993) Biochim. Biophys. Acta 1141, 221-230], with dipolar coupling between Q(A)-. and 3D of -0.125 mT.