The 1064-nm excited Fourier transform Raman spectra have been measured for two kinds of whole living cells of photosynthetic bacteria, Rhodobacter sphaeroides G1C and R26 mutants, to investigate in situ structures of photosynthetic pigments, bacteriochlorophyll-a
(BChl-a) and neurosporene (the only carotenoid included in the G1C mutant). The 1064-nm excited spectra consist of contributions from both neurosporene and BChl-a in the light harvesting (LH) complexes (G1C) or from BChl-a alone in the LH complexes (R26). The pattern of
the 1064-nm excited spectrum of BChl-a in the LH complexes, whose Raman bands are pre-resonance enhanced via its Qy band, is dramatically different from that of its 355-nm excited spectrum, whose Raman bands are resonance enhanced via the B bands; for example, a band at
1606 cm−1 due to a Ca--Cm stretching mode of BChl-a, which is the most intense in the 355-nm excited spectrum, is barely observed in the 1064-nm excited spectrum. The frequency of the above band indicates that BChl-a in the LH complexes is five-coordinate.
Bands due to C=O stretching modes of the 9-keto and 2-acetyl groups of BChl-a appear clearly near 1665 and 1640 cm−1, respectively, in the 1064-nm excited spectra. The frequencies of these C=O stretching bands suggest that most of the 9-keto and 2-acetyl groups of BChl-a
in the complexes are involved in intermolecular interaction with the proteins. Bands assignable to Ca--N and Ca--Cb stretching modes, which are, in general, very weak in the 355-nm excited spectra, appear strongly in the 1064-nm excited spectra, implying that their bond lengths
are changed sizably in the electronic transitions corresponding to the Qy bands.
Department of Chemistry, School of Science, Kwansei Gakuin University, Uegahara, Nishinomiya 662, Japan 2:
Analytical Instruments Division, JEOL Ltd., Akishima 196, Japan
Publication date: March 1, 1992
More about this publication?
The Society publishes the internationally recognized, peer reviewed journal, Applied Spectroscopy, which is available both in print and online. Subscriptions are included with membership or can be purchased by institutional or corporate organizations. Abstracts may be viewed free of charge. Previously published as Bulletin (Society for Applied Spectroscopy)