Light‐induced Fourier transform infrared (FTIR) spectroscopic investigations of primary reactions in photosystem I and photosystem II

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Abstract
Light‐induced Fourier transform infrared (FTIR) difference spectroscopy has been applied for the first time to primary reactions in green plant photosynthesis. Photooxidation of the primary electron donor (P700) in photosystem I‐enriched particles as well as in thylakoids, and photoreduction of the pheophytin (Pheo) intermediary electron acceptor in photosystem II‐enriched particles, have led to reproducible difference spectra. In the spectral range investigated (between 1800 and 1000 cm−1) several bands are tentatively attributed to changes in intensity and position of the keto and ester carbonyl vibrations of the chlorophyll or Pheo molecule(s) involved. For some of these groups, possible interpretations in terms of changes of their environment or type of bonding to the protein are given. The intensity of the differential features in the amide I and amide II spectral region allows the exclusion of the eventuality of large protein conformational changes occurring upon primary charge separation.