Resonance Raman studies on the structure of bacteriochlorophyll c in chlorosomes from Chloroflexus aurantiacus

Resonance Raman spectra of chlorosomes isolated from the thermophilic green photosynthetic bacterium Chloroflexus aurantiacus have been obtained with several excitation wavelengths from 441.6 to 514.5 nm. Resonance Raman spectra of bacteriochlorophyll (BChl) c isolated from C. aurantiacus cells have also been observed. The C=C stretching frequencies of BChl c in the chlorosomes were found to be at 1,556 (strong) and 1,544 (shoulder) cm-1, which correspond to those expected for the 5-coordinated BChl c. The C-9 carbonyl resonance Raman frequency was found at 1,642 cm-1, indicating that this group is either hydrogen-bonded to an Mg-coordinated hydroxyl group or coordinated to the Mg ion.