Abstract
Photosynthetic reaction centers (RCs) fromRhodobacter sphaeroides capture solar energy by electron transfer from primary donor D to quinone acceptor QB through the active A branch of electron acceptors. The light-induced electron paramagnetic resonance (EPR) spectrum from native RCs that had Fe2+ replaced by Zn2+ was investigated at cryogenic temperature (80 K, 35 GHz). In addition to the light-induced signal due to the formation of D+.Q −.A observed previously, a small fraction (ca. 5%) of the signal displayed very different characteristics. The signal was absent in RCs in which the QB was displaced by the inhibitor stigmatellin. Its decay time (τ=6 s) was the same as observed for D+.Q −.B in mutant RCs lacking QA, which is significantly slower than for D+.Q −.A (τ=30 ms). Its EPR spectrum was identical to that of D+.Q −.B . The quantum efficiency for forming the major component of the signal was the same as that found for mutant RCs lacking QA (ϕ=0.2%) and was temperature independent. These results are explained by direct photochemical reduction of QB via B branch electron transfer in a small fraction of native RCs.
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Paddock, M.L., Isaacson, R.A., Abresch, E.C. et al. Light-induced EPR spectra of reaction centers fromRhodobacter sphaeroides at 80 K: Evidence for reduction of QB by B branch electron transfer in native reaction centers. Appl. Magn. Reson. 31, 29–43 (2007). https://doi.org/10.1007/BF03166246
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DOI: https://doi.org/10.1007/BF03166246