FUNCTION OF HELIOBACTERIA- AND GREEN SULFUR BACTERIA-TYPE REACTION CENTERS

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In the reaction center complex (PS-C) from the green sulfur bacterium Chlorobium tepidum, A_0 and three Fe-S clusters function on the accepter side of the electron transfer chain and two molecules of cyt c-551 on the donor side. From multiple-flash-induced spectroscopy, we could not find any possibilities of functioning of quinone in the main electron transfer chain. On the donor side, the reduction rate of P840^+ after the first flash differed from that after the second flash, which was adequately explained by a functionally equivalent two cyt c-551 model. From the difference spectra of PS-C after the 1^<st>, 2^<nd> and the 3^<rd> flash, functioning of three Fe-S clusters was confirmed, corroborating the non-involvement of quinines on the acceptor side in the electron transfer chain, From the rereduction rates of P840^+, the rates of charge recombination between P840^+ and three Fe-S clusters and those of the leak of electron to the reaction mdeium were estimated. Analyses of the results indicate that the E_0 value of the most exposed Fe-S cluster is not the highest among the three. Four ferredoxins (Fd) were purified from C.tepidum. All of these Fd supported very high rate of NADP^+ photoreduction in the presence of PS-C from C.repidum and FNR from spinach, although their affinities differ each other.RC (PS-H) from Heliobacillus mobilis was solubilized with a detergent, and partially purified by sucrosedensity centrifugation, and by chromatography. The PS-H preparation contained several polypeptides, showed a low Fd-reducing activity, and was sensitive to oxygen. Two Fd were purified from the bacterium. One of them had high affinity with PS-C and the other low affinity.