Rates of the initial two steps of electron transfer in reaction centers from Rhodobacter sphaeroides as determined by singular-value decomposition followed by global fitting

The pump–probe spectral data matrices of reaction centers from Rhodobacter sphaeroides R26.1 and 2.4.1 in the 650–1265 nm region, that have been obtained by excitation of P at 868 nm with ∼0.1 ps pulses, were analyzed by singular-value decomposition followed by global fitting by the use of a three-component sequential model. The species-associated difference spectra showed the P∗BH → P+B−H → P+BH− sequential electron transfer and the rates of electron transfer were determined to be (1.9 ps)−1 and (2.7 ps)−1 for the first and the second steps, respectively. The P∗BH ⇌ P+B−H reversible electron transfer was also identified.