STEP-SCAN FT-IR SPECTROSCOPY OF ELECTRON-TRANSFER IN THE PHOTOSYNTHETIC BACTERIAL REACTION-CENTER

Step-scan light-induced FT-IR difference spectra (1800 1200 cm-1) of Rhodobacter sphaeroides photosynthetic bacterial reaction centers at low temperature and with a 10-mus time resolution are presented. The molecular changes and relaxation processes accompanying the photoxidation of the primary electron donor (P) are already present 10 mus after excitation. The photoconversion of P to the triplet state gives rise to characteristic IR absorption changes which decay with a half-time of 130 mus. A negative band at 1695 cm-1 and a positive one at 1670 cm-1 are assigned to the 9-keto carbonyl of bacteriochlorophyll in the states P and P-3, respectively.