PHOTOSYNTHESIS, REACTION CENTER, MEMBRANE PROTEIN, PHOTOSYNTHETIC REACTION CENTER, ELECTRON TRANSPORT, BACTERIOCHLOROPHYLL, IRON, MEMBRANE, MAGNESIUM, TRANSPORT, CHROMOPHORE, CHLOROPHYLL, METAL-BINDING, TRANSMEMBRANE 2WX5 HEXA-COORDINATION OF A BACTERIOCHLOROPHYLL COFACTOR IN THE RHODOBACTER SPHAEROIDES REACTION CENTRE