Light-Harvesting Function in the Diatom Phaeodactylum tricornutum: I. Isolation and Characterization of Pigment-Protein Complexes |
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| Authors: | Owens T G Wold E R |
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| Affiliation: | Section of Plant Biology, Cornell University, Ithaca, New York 14853. |
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| Abstract: | Three pigment-protein complexes were isolated from the marine diatom Phaeodactylum tricornutum (Bohlin) by treatment of thylakoid membrane fragments with 1% Triton X-100 at 4°C followed by centrifugation on sucrose density gradients. The major complex contains chlorophyll a, c1, c2, and the carotenoid fucoxanthin (chlorophyll a: c1: c2: fucoxanthin = 1.0: 0.09: 0.28: 2.22) bound to an apoprotein doublet of 16.4 and 16.9 kilodaltons. This complex accounts for >70% of the total pigment and 20 to 40% of the protein in the thylakoid membranes. Efficient coupling of chlorophyll c and fucoxanthin absorption to chlorophyll a fluorescence supports a light-harvesting function for the complex. A minor light-harvesting complex containing chlorophyll a, c1, and c2 but no fucoxanthin (chlorophyll a: c1: c2 = 1.0: 0.23: 0.26) was also isolated at Triton: chlorophyll a ratios between 20 and 40. These pigments are bound to a similar molecular weight apoprotein doublet. The third complex isolated was the P700-chlorophyll a protein, the reaction center of photosystem I, which showed characteristics similar to those isolated from other plant sources. The yield of the chlorophyll a/c-fucoxanthin complex was shown to respond strongly to changes in light intensity during growth, accounting for most of the changes in cellular pigmentation. |
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