HIGHLY PURIFIED PHOTOSYNTHETIC REACTION CENTER (PSCA/CYTOCHROME C551)2 COMPLEX OF THE GREEN SULFUR BACTERIUM CHLOROBIUM LIMICOLA

The photosynthetic reaction center (RC) complex that forms a homodimer of core and cytochrome c subunits was isolated form Chlorobium limicola f. thiosulfatophilum, strain Larsen. The complex showed only two subunit bands at 68 (PscA core) and 21 kDa (cytochrome c{sub 551}) on SDS-PAGE analysis, indicating the complete deletion of the light-harvesting bacteriochlorophyll {alpha} (BChl {alpha}) protein as well s the iron-sulfur protein. It contained 27 {plus_minus} 3 molecules of BChl {alpha}, 7 {plus_minus} 1 Chl-670, 3 {plus_minus} 1 carotenoids, and 1.6 {plus_minus}0.1 c-type hemes per the primary electron donor P840. The complex showed a light-induced charge separation and recombination between P840 and the acceptor Chl-670 at 77 K as follows: P840{sup *}Chl-670{r_arrow}P840{sup +}Chl-670{sup {minus}}{r_arrow}P840{sup T}Chl-670{r_arrow}P840 Chl-670. Pigment compositions and their function in the (PscA/cytochrome c{sub 551}){sub 2} complex were studied by absorption, circular dichroism, and fluorescence spectroscopy 36 refs., 8 figs.