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Light-Harvesting Function in the Diatom Phaeodactylum tricornutum: I. Isolation and Characterization of Pigment-Protein Complexes

Thomas G. Owens and Evarina R. Wold
Plant Physiology
Vol. 80, No. 3 (Mar., 1986), pp. 732-738
Stable URL: http://www.jstor.org/stable/4269823
Page Count: 7
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Light-Harvesting Function in the Diatom Phaeodactylum tricornutum: I. Isolation and Characterization of Pigment-Protein Complexes
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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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