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

Using a mild detergent, octyl sucrose, light-harvesting fucoxanthin-Chla/c-protein complexes of a brown alga, Petalonia fascia, wereisolated in the form of supramolecular assemblies. Negativelystained images of these assemblies (FCPAs) were extremely uniformin size and shape. Each was discoidal in shape, being 11.2 nmin diameter and 10.2 nm in height, with a small pit at the centerof disc. From the sedimentation rate (S_{20, w} = 21.6) and theobserved dimensions, the molecular mass (Mr) of FCPA was calculatedas about 697?10³, and each FCPA was deduced to contain 128 moleculesof Chl a 27 of Chl c, 69 of fucoxanthin and 8 of violaxanthin.Fresh FCPA showed highly efficient transfer of excitation energyfrom fucoxanthin to Chl a but the energetic coupling was disruptedon storage with accompanying distortion of fine structures.Given the occurrence of similar supramolecular assemblies offucoxanthin-chlorophyll a/c-protein complexes in another brownalga, Dictyota dichotoma Katoh et al. (1989) Biochim. Biophys.Acta 976: 233], the molecular assemblies of fucoxanthin-Chla/c-protein complexes is assumed to be common to the light harvestingsystems in all brown algae. (Received December 28, 1989; Accepted March 5, 1990)