The effect of detergent on the structure and composition of chlorosomes isolated from Chloroflexus aurantiacus |
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Authors: | Mette Miller David Simpson Thomas E. Redlinger |
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Affiliation: | (1) Institute of Biochemistry, Odense University, Campusvej 55, DK-5230 Odense M, Denmark;(2) Department of Physiology, Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-2500 Copenhagen, Denmark;(3) Present address: Biochemistry Department, University of Massachusetts, 01003 Amherst, MA, USA |
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Abstract: | Isolated chlorosomes, treated with the detergent lithium dodecyl sulfate (LDS), can be separated into two green fractions by agarose gel electrophoresis. One fraction contains chlorosomes with a full complement of proteins and antenna BChl c absorbing at 740 nm, but with a more spherical form than the normal ellipsoid shape observed in control chlorosomes. The second fraction was completely devoid of proteins but had a similar absorption spectrum. Electron micrographs of the protein-free fraction indicated the presence of stain-excluding spheres with overall dimensions resembling those of intact chlorosomes (40–100 nm). These spheres are probably micelles of BChl c liberated from the chlorosomes during the detergent treatment, since similar structures could be produced when purified BChl c, dissolved in 1-hexanol, was dispersed in buffer, producing an aggregate absorbing at 742 nm. These results suggest that the chlorosome proteins are not required to produce an arrangement of BChl c chromophores which gives rise to a 740 nm absorption peak resembling that of intact chlorosomes. It seems probable, however, that proteins have a role in determining the overall shape of the chlorosome. Treatment with cross-linking reagents did not prevent the detergent-induced changes in chlorosome morphology.Abbreviations BChl bacteriochlorophyll - DSP dithiobis-succinimidyl-2-propionate - EM electron microscopy - LDS lithium dodecyl sulfate - MGDG monogalactosyl diacylglycerol - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis |
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Keywords: | BChl c aggregates cross-linking green bacteria light-harvesting antenna pigment organization ultrastructure |
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