Participation of spirilloxanthin in excitation energy transfer in reaction centers from purple bacteria Rhodospirillum rubrumстатьяИсследовательская статья
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Аннотация:The femtosecond dynamics of energy transfer from light-excited spirilloxanthin (Spx) to bacteriochlorophyll (BChl) a in the reaction centers (RCs) of purple photosynthetic bacteria Rhodospirillum rubrum was studied. According to crio-electron microscopy data, Spx is located near accessory BChl a in the B-branch of cofactors. Spx was excited by 25 fs laser pulses at 490 nm, and difference absorption spectra were recorded in the range 500–700 nm. To reveal the dynamics of individual states, we applied global analysis using different kinetic schemes. We found that the energy transfer Spx → BChl a occurs during 0.22 ps with a low efficiency of ~31%. The monomeric BChl a acts as the primary energy acceptor, presumably in the B-branch of cofactors. Then the energy is transferred to the BChl a dimer within 0.25 ps and subsequently used for charge separation. As a result of internal conversion in Spx, the majority (~69%) of the excitation energy transfers in 0.2 ps from the singlet-excited state S2 to the states S1 and S*, which, in turn, relax to the ground state in 1.5 and 9 ps, respectively. We showed that the S1 and S* states in Spx are not involved in energy transfer to BChl a. The found parameters of energy transfer Spx→BChl a turned out to be close to those in the light-harvesting complexes LH1 of Rhodospirillum rubrum. The sequence of events in Spx after its excitation is discussed.
