ISOLATION AND PROPERTIES OF PHOTOCHEMICALLY ACTIVE REACTION-CENTER COMPLEXES FROM THE GREEN SULFUR BACTERIUM PROSTHECOCHLORIS-AESTUARII

A new and rapid procedure was developed for the isolation of the react ion center core (RCC)complex from the green sulfur bacterium Prostheco chloris aestuarii. Reaction center preparations containing the Fenna M atthews Olson (FMO) protein were also obtained. The procedure involved incubation of broken cells with the detergents Triton X-100 and SB12, sucrose gradient centrifugation and hydroxyapatite chromatography. Th ree different pigment protein complexes were obtained: one containing (about) three FMO trimers per RCC, one with one FMO per RCC and one co nsisting of RCC only. The last one contained polypeptides with apparen t molecular masses of 64 kDa (pscA) and 35 kDa (pscB, the F-A/F-B, FeS subunit), but no cytochrome. Bacteriochlorophyll a and the chlorophyl l a isomer functioning as primary electron acceptor were present at a ratio of 4.8:1. The complexes were also characterized spectroscopicall y and in terms of photochemical activity, at room temperature as well as at cryogenic temperatures. Illumination caused oxidation of the pri mary donor P840, with the highest activity in the RCC complex (Delta A (840)/A(810) = 0.06) At room temperature in the RCC complex essentiall y ail of the P840(+) produced in a flash was re-reduced slowly in the dark (several seconds). At low temperatures (150-10 K) a tripler was f ormed in a fraction of the reaction centers, presumably by a reversal of the charge separation, whereas in others P840(+) formed in the ligh t was re-reduced in 40-50 ms.