Giant circular dichroism of chlorosomes fromChloroflexus aurantiacus treated with 1-hexanol and proteolytic enzymes |
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Authors: | Rainer P Lehmann René A Brunisholz Herbert Zuber |
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Institution: | (1) Institut für Molekularbiologie und Biophysik, ETH-Hönggerberg, 8093 Zürich, Switzerland |
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Abstract: | The circular dichroism (CD) spectrum of isolated chlorosomes fromChloroflexus aurantiacus showed a conservative, S-shaped signal with a negative maximum at 723 nm, a positive maximum at 750 nm and a zero-crossing at 740 nm. Proteolytic treatment of chlorosomes with trypsin at 37°C did not change the CD signal or the absorption spectrum in contrast to treatment with proteinase K, where a twofold increase in rotational strength and a slight decrease of the absorption band at 740 nm were observed. Treatment with saturating 1-hexanol concentrations resulted in a blue shift of the absorption band at 740 nm as well as in changes of the CD spectrum. These changes reversed when the sample was diluted to half the saturating 1-hexanol concentration. In contrast to that, we observed an irreversible formation of a giant CD signal using the combination of 1-hexanol and proteinase K treatment. Electron micrographs of chlorosomes treated with both 1-hexanol and proteinase K showed large aggregates of multiple chlorosome size. By comparison of proteinase K induced effects with trypsin effects it appeared that the 5.7 kDa polypeptide has a structural role in the organisation of BChlc in the chlorosome. |
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Keywords: | bacteriochlorophyllc green photosynthetic bacteria pigment-protein interaction |
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