PHOTOPHYSICS OF PHOTOSYNTHESIS - STRUCTURE AND SPECTROSCOPY OF REACTION CENTERS OF PURPLE BACTERIA

The fundamental photochemical reaction of photosynthetic energy conver sion, which transforms the photon energy of light in chemical free ene rgy, takes places in a membrane-bound, pigmented reaction center prote in (RC). We examine here the structure-function relationships of this uniquely efficient process. First, the RC is discussed in relation to the overall photosynthetic apparatus. Second, we highlight the X-ray d iffraction analysis of two bacterial RCs, discussing the problems asso ciated with the analysis of a non-water-soluble protein of molecular w eight over 120 kDa. The structure of the polypeptide chains in the RC- protein, and the configuration of the cofactors non-covalently bound t o the polypeptide scaffolding, is reviewed in detail. Third, we presen t a detailed account of investigations on the functioning of the RC wi th a number of optical and magnetic resonance spectroscopic techniques , with emphasis on the relation between structure and function. The re sults for RCs of purple bacteria, green bacteria and the two plant pho tosystems are compared, and discussed in the framework of current theo ries of photosynthetic electron transport.