EXCITED-STATES AND CHARGE SEPARATION IN MEMBRANES OF THE GREEN SULFURBACTERIUM PROSTHECOCHLORIS-AESTUARII

Time-resolved absorbance changes were measured in isolated membranes, depleted of chlorosomes, and in the Fenna-Matthews-Olson (FMO) complex of the green sulfur bacterium Prosthecochloris aestuarii. The isolate d FMO complex showed a biphasic decay of excited bacteriochlorophyll a (BChl a) with time constants of about 80 and 1400 ps. Approximately t he same time constants were observed upon excitation of isolated membr anes together with a component of about 30 ps. It is concluded that th e efficiency of energy transfer from the FMO to the core complex is ve ry low, in agreement with earlier measurements of the efficiency of ch arge separation. The 30 ps decay component is ascribed to trapping of the excitation energy from the core BChl a by the reaction center.