Novel multipulse saturation spectroscopy for quantum yield determination of charge separation in modified photosynthetic reaction centers

We describe a method for the quantum yield determination of transmembrane charge separation in bacterial reaction centers (RC) that is independent of the content of quinone at the QA site and of loss channels in any time domain. We applied the method to RCs, where the energy of the radical pair P+BA− is lowered by replacing BA site bacteriochlorophyll against 132–OH–Ni–bacteriochlorophyll (NiA-RC). The quantum yield of charge separation Y(P+QA−) was 0.65±0.02 at 120 K. It is suggested that charge recombination from P+BA− is the source for the quantum yield loss. The occupancy of the QA site was determined to be 0.99±0.03.