STEP-SCAN FTIR SPECTROSCOPY RESOLVES THE Q(A)(-)Q(B)-]Q(A)Q(B)(-) TRANSITION IN RB-SPHAEROIDES R26 REACTION CENTERS

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 p reviously assigned to Q(A/B) and Q(A/B)(-) vibrations, respectively (B rudler et al. 1994; Brudler et al. 1995; Breton and Nabedryk 1996), ca n be resolved with this new technique. In addition, the three small po sitive bands in the spectral region of the carboxylic C=O stretching m odes of acidic amino acid side chains are also resolved at 1730, 1719 and 1704 cm(-1). A global fit analysis yields two exponentials with ha lf-times of 150 mu s and 1.2 ms in agreement with IR spectroscopic stu dies at single wavenumbers (Hienerwadel et al. 1995), in the UV/VIS an d near IR (Tiede et al. 1996, Li et al. 1996). The establishement of t he step-scan technique enables a new approach to elucidate the molecul ar mechanism of this transition.