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Diatoms differ from higher plants by their antenna system, in terms of both polypeptide and pigment contents. A rapid isolation procedure was designed for the membrane-intrinsic light harvesting complexes (LHC) of the diatom Phaeodactylum tricornutumto establish whether different LHC subcomplexes exist, as well to determine an uneven distribution between them of pigments and polypeptides. | ềFEBS Journal The light-harvesting antenna of the diatom Phaeodactylum tricornutum Evidence for a diadinoxanthin-binding subcomplex Gerard Guglielmi Johann Lavaud Bernard Rousseau Anne-Lise Etienne Jean Houmard and Alexander V. Rubant Organismes Photosynthetiques et Environnement CNRS Departement de Biologie Ecole Normale Superieure Paris France Keywords diatom fucoxanthin light-harvesting complex photoprotection xanthophyll cycle Correspondence G. Guglielmi Organismes Photo-synthetiques et Environnement UMR 8541 CNRS Departement de Biologie Ecole Normale Superieure 46 rue d Ulm 75230 Paris cedex 05 France Fax 33 1 44 32 39 41 Tel 33 1 44 32 35 30 E-mail ggugliel@biologie.ens.fr Present address Pflanzliche Okophysiologie Fachbereich Biologie Universitat Konstanz Germany TThe Robert Hill institute Department of Molecular Biology and Biotechnology University of Sheffield UK Diatoms differ from higher plants by their antenna system in terms of both polypeptide and pigment contents. A rapid isolation procedure was designed for the membrane-intrinsic light harvesting complexes LHC of the diatom Phaeodactylum tricornutum to establish whether different LHC subcomplexes exist as well to determine an uneven distribution between them of pigments and polypeptides. Two distinct fractions were separated that contain functional oligomeric complexes. The major and more stable complex w 75 of total polypeptides carries most of the chlorophyll a and almost only one type of carotenoid fucoxanthin. The minor complex carrying w 10-15 of the total antenna chlorophyll and only a little chlorophyll c is highly enriched in diadinoxanthin the main xanthophyll cycle carotenoid. The two complexes also differ in their polypeptide composition suggesting specialized functions within the antenna. The diadinoxanthin-enriched complex could be where the de-epoxidation of diadinoxanthin into diatoxanthin mostly occurs. Note A website is available http www.biologie. ens.fr opeaec Received 31 May 2005
