In vivo states and functions of carotenoids in an aerobic photosynthetic bacterium,Erythrobacter longus |
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Authors: | Takumi Noguchi Hidenori Hayashi Keizo Shimada Shinichi Takaichi Mitsuo Tasumi |
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Institution: | (1) Department of Chemistry, Faculty of Science, The University of Tokyo, 113 Bunkyo-ku, Tokyo, Japan;(2) Department of Biology, Faculty of Science, Tokyo Metropolitan University, Minamiosawa, 192-03 Hachioji-shi, Tokyo, Japan;(3) Biological Laboratory, Nippon Medical School, Kosugi-cho 2, 211 Nakahara-ku, Kawasaki, Japan;(4) Present address: Solar Energy Research Group, The Institute of Physical and Chemical Research (RIKEN), 351-01 Wako-shi, Saitama, Japan;(5) Present address: National Institute for Basic Biology, 444 Okazaki, Aichi, Japan |
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Abstract: | In vivo states and functions of carotenoids in the membranes and the isolated RC-B865 pigment-protein complexes from an aerobic photosynthetic bacterium, Erythrobacter longus, are investigated by means of fluorescence excitation and resonance Raman (RR) spectra. Erythroxanthin sulfate, a dominant carotenoid species in the membranes (>70%), is found not to transfer the absorbed light energy to bacteriochlorophyll (Bchl), and its RR spectra are similar between the in vivo and in vitro states. These observations indicate that erythroxanthin sulfate does not interact with either Bchl or proteins in the membranes, and suggest that its function may be limited to photoprotection by quenching the harmful singlet oxygen. On the other hand, two other carotenoid species contained in the isolated RC-B865 complexes, zeaxanthin and bacteriorubixanthinal, have a high efficiency of energy transfer to Bchl (88±5%). The RR spectra of these two carotenoids, each of which can be selectively obtained by choosing the excitation wavelength, show some characteristics of interactions with proteins or Bchl.Abbreviations Bchl
bacteriochlorophyll a
- FWHM
full width at half maximum
- PAGE
polyacrylamide gel electrophoresis
- RC
reaction center
- RR
resonance Raman
- SDS
sodium dodecyl sulfate |
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Keywords: | aerobic photosynthetic bacteria carotenoid energy transfer Erythrobacter longus fluorescence excitation spectra resonance Raman spectra |
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