Step-scan FTIR spectroscopy resolves the QA-QB→QAQB- transition in Rb-sphaeroides R26 reaction centres

It is shown that step-scan Fourier transform infrared spectroscopy can be applied to resolve the Q(A) (-)Q(B) --> Q(A)Q(B)(-) transition in Rhodobacter sphaeroides reaction centres with a 5 mu s time resolution. In the mid-infrared region (1900 - 1200 cm(-1)), transient signals previously assigned to Q(A/B) and Q(A/B)(-) vibrations, respectively (Brudler et al. 1994; Brudler et al. 1995; Breton and Nabedryk 1996), can be resolved with this new technique. In addition, the three small positive bands in the spectral region of the carboxylic C=O stretching modes of acidic amino acid side chains are also resolved at 1730, 1719 and 1704 cm(-1). A global fit analysis yields two exponentials with half-times of 150 mu s and 1.2 ms in agreement with IR spectroscopic studies at single wavenumbers (Hienerwadel et al. 1995), in the UV/VIS and near IR (Tiede et al. 1996, Li et al. 1996). The establishement of the step-scan technique enables a new approach to elucidate the molecular mechanism of this transition.