[15] Bacterial Reaction Center (RC) and Photoreceptor complex (PRC) Preparations

This chapter discusses bacterial reaction center (RC) and photoreceptor complex (PRC) preparations. Three kinds of preparations are discussed in the chapter. The “RE” is the term used to describe those minimal components (bacteriochlorophyll, bacteriopheophytin, ubiquinone, protein, etc.) which are required for carrying out the primary photochemical event. The “PRC” is the term used for a preparation that contains the reaction center, a specific quantity of antenna pigments (bacteriochlorophyll and carotenoids), and specific protein components that bind the antenna pigments. The third term is that which describes a light-harvesting (LH) pigment–protein complex and represents an antenna bacteriochlorophyll and/or carotenoid complex, which contains a specific protein component but no reaction center. The standard tests for RC activity in preparations from photosynthetic bacteria have been the demonstration at low temperature of appropriate light-induced absorbance changes and an electron spin resonance (ESR) signal characteristic of formation of the primary electron donor bacteriochlorophyll cation radical with a quantum yield near 1.0. The chapter also describes the composition of the PRC, prepared from Rhodospirillum rubrum, and compares it with the chromatophore fraction from which it was prepared.