Supramolecular Assembly of Fucoxanthin-Chlorophyll-Protein Complexes Isolated from a Brown Alga, Petalonia fascia. Electron Microscopic Studies

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Using a mild detergent, octyl sucrose, light-harvesting fucoxanthin-Chl a/c-protein complexes of a brown alga, Petalonia fascia, were isolated in the form of supramolecular assemblies. Negatively stained images of these assemblies (FCPAs) were extremely uniform in size and shape. Each was discoidal in shape, being 11.2 nm in diameter and 10.2 nm in height, with a small pit at the center of disc. From the sedimentation rate (S_<20,w> = 21.6) and the observed dimensions, the molecular mass (Mr) of FCPA was calculated as about 697 × 10^3, and each FCPA was deduced to contain 128 molecules of Chl a, 27 of Chl c, 69 of fucoxanthin and 8 of violaxanthin. Fresh FCPA showed highly efficient transfer of excitation energy from fucoxanthin to Chl a, but the energetic coupling was disrupted on storage with accompanying distortion of fine structures. Given the occurrence of similar supramolecular assemblies of fucoxanthin-chlorophyll a/c-protein complexes in another brown alga, Dictyota dichotoma [Katoh et al. (1989) Biochim. Biophys. Acta 976: 233], the molecular assemblies of fucoxanthin-Chl a/c-protein complexes is assumed to be common to the light harvesting systems in all brown algae.
日本植物生理学会の論文