Comparative Study of Spectral and Kinetic Properties of Electron Transfer in Purple and Green Photosynthetic Bacteria

The spectral properties in the visible and near infrared regions of reaction centers of the purple bacterium Rhodobacter sphaeroides and the green nonsulfur bacterium Chloroftexus aurantiacus are determined by special interaction between 4 molecules of BChl a and 2 molecules of bacteriopheophytin (BPh) a in Rb. sphaeroides (Straley et at., 1973) and 3 molecules of BChl a and 3 molecules of BPh a in Cf. aurantiacus (Vasmel et at., 1966). These molecules are in L- and M-protein subunits of Rb. sphaeroides (Allen et al., 1986) and bound to the two protein subunits with molecular mass of 26 kDa in Cf. aurantiacus RCs (Feick and Fuller, 1984). Two BChl a molecules form the special pair, the primary electron donor Pr absorbing at 670 nm (900 nm at 77 K) in both species. In Rb. sphaeroides RCs the L- as well as M-protein subunits contain one BChl a and one BPh a, BL and HL, and BM and HM, respectively (Allen et al., 1986). The pigments form two prosthetic chains: P-BL-HL-Qa and P-BM-HM-Qb where Qa and Qb are the primary and secondary quinones. Only one chain P-BL-HL-Qa is photochemically active (Shuvalov et al., 1986a).