FTIR Spectroscopic Investigations of the Intermediary Electron Acceptor Photoreduction in Purple Photosynthetic Bacteria and Green Plants

Abstract

We have recently demonstrated that light-induced Fourier transform infrared (FTIR) spectroscopy can be applied to bacterial reaction centers -RCs- (1–3) as well as to photosystems from green plants (4) in order to detect changes in the molecular interactions between the pigments involved in the primary charge separation and their anchoring sites in the protein. Using FTIR difference spectroscopy the sensitivity is high enough to detect perturbations in the vibrational modes of chlorophylls and protein groups in a large complex such as a RC. For both primary electron donor photooxidation and intermediary electron acceptor photoreduction we have reported very specific absorbance changes (1–4). However, due to the non selectivity of IR spectroscopy, the FTIR signals might arise from the pigments, the protein (peptide and side chains groups), the lipids and even bound water molecules. Thus, a precise assignment of the FTIR absorbance changes to chemical bonds requires further investigations using model compounds radicals of the isolated chlorophylls as well as isotope-substituted material.