PRIMARY PHOTOREACTIONS IN COMPLEX CYTOCHROME-P-890.P760 (BACTERIOPHEOPHYTIN760) OF CHROMATIUM-MINUTISSIMUM AT LOW REDOX POTENTIALS

Experimental evidence for electron transfer, photosensitized by bacteriochlorophyll, from cytochrome c to a pigment complex P-760 (involving bacteriopheophytin-760 and bacteriochlorophyll-800) in the reaction centers of C. minutissimum was described. This photoreaction occurs between 77.degree. and 293.degree. K at a redox potential of the medium between -250 and -530 mV. Photoreduction of P-760 is accompanied by development of a wide absorption band at 650 nm and an EPR signal with g = 2.0025 .+-. 0.0005 and linewidth of 12.5 .+-. 0.5 G, which are characteristic of the pigment radical anion. The photoreduction of P-760 probably occurs under the interaction of reduced cytochrome c with the reaction center state P+-890.cntdot.P--760 which is induced by light. The existence of short-lived state P+-890.cntdot.P--760 is indicated by the recombination luminescence with activation energy of 0.12 eV and .tau.1/2 [lifetime] .ltoreq. 6 ns. This luminescence is excited and emitted by bacteriochlorophyll and disappears when P-760 is reduced. At low redox potentials, the flash-induced absorbance changes related to the formation of the carotenoid triplet state with .tau.1/2 [half time] = 6 .mu.s at 20.degree. C are observed. This state is not formed when P-760 is reduced at 293.degree. and 160.degree. K. This state is probably formed from the reaction center state P+-890.cntdot.P--760, which may be a primary product of light reaction in the bacterial reaction centers and which is probably identical with the state PF described in recent works.