Abstract
Rapid-scan FTIR difference spectroscopy was used to investigate light-induced reduction of the ubiquinone QB ,a nd the oxidation kinetics of QB − and QH2 by external mediators in isolated reaction centers (RCs) from R. sphaeroides. As redox mediators, a Ferrocyanide/N,N,N � ,N � -tetramethyl-p-phenylenediamine (TMPD) mixture and an Ascorbate/2,3,5,6-tetramethyl- p-phenylenediamine (DAD) mixture are compared. Results show that TMPD red rapidly reduces the photoproduced P870 + primary donor. The process is fast enough to record rapid-scan FTIR spectra devoid of P870 + bands down to 260 K. Results show also that TMPD ox oxidises both QB − and QH2 faster than DAD ox . In particular, QB − is oxidised faster than QH2 at all temperatures studied. Results are discussed in the framework of time-resolved infrared studies on R. sphaeroides RCs, showing advan- tages/drawbacks of the proposed experimental approach.
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