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| - Polarized Fluorescence of Aggregated Bacteriochlorophyll c and BaseplateBacteriochlorophyll a in Single Chlorosomes Isolated fromChloroflexus aurantiacus
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| - The polarization anisotropy of fluorescence from single chlorosomes isolated from a greenfilamentous bacterium, Chloroflexus aurantiacus, was measured using a confocal laser microscope at 13K. Each single chlorosome that is floating in a frozen solvent exhibited strong polarization anisotropy offluorescence. We calculated the degrees of fluorescence polarization for 51 floating single chlorosomes.The value ranged from 0.1 to 0.76 for the BChl-c aggregate in the core chlorosomes and from 0 to 0.4for the energy acceptor BChl-a in the baseplate protein in the outer membrane. The shifts in polarizationangles between the two emission bands were distributed over all the possible values with a sharp peakaround 90°, suggesting the perpendicular orientation between the transition dipoles of the fluorescenceemission from the BChl-c aggregate and that from BChl-a. A simulation assuming a random orientationof chlorosomes reproduced the experimental results exactly. The analysis further indicated the appreciablecontribution of the transition dipole of BChl-c that has an orientation perpendicular to the major polarizationaxis in each chlorosome. Small values of the degrees of polarization implied the BChl-a transition dipoleto be somewhat tilted with respect to the normal of the cytoplasmic membrane to which chlorosomes areattached. These conclusions can be obtained only by observing the fluorescence of single chlorosomes.
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