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Photosystem I from the unusual cyanobacterium Gloeobacter violaceus Mangels, D.; Kruip, J.; Berry, S.; Rögner, M.; Boekema, E.J.; Koenig, F. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Key words: antenna system, electron microscopy, fluorescence, light harvesting, photosynthesis, plasma membrane AbstractPhotosystem I (PS I) from the primitive cyanobacterium Gloeobacter violaceus has been purified and characterised. Despite the fact that the isolated complexes have the same subunit composition as complexes from other cyanobacteria, the amplitude of flash-induced absorption difference spectra indicates a much bigger antenna size with about 150 chlorophylls per P700 as opposed to the usual 90. Image analysis of the PS I preparation from Gloeobacter reveals that the PS I particles exist both in a trimeric and in a monomeric form and that their size and shape closely resembles other cyanobacterial PS I particles. However, the complexes exhibit a higher molecular weight as could be shown by gel filtration. The preparation contains novel polypeptides not related to known Photosystem I subunits. The N-terminal sequence of one of those polypeptides has been determined and reveals no homology to known or hypothetical proteins. Immunoblotting shows a cross-reaction of three of the polypeptide bands with an antibody raised against the major LHC from the diatom Cyclotella cryptica. Electron microscopy reveals a novel T-shaped complex which has never been observed in any other cyanobacterial PS I preparation. 77 K spectra of purified PS I show an extreme blue-shift of the fluorescence emission, indicating an unusual organisation of the PS I antenna system in Gloeobacter.Abbreviations: PS -photosystem; Chl -chlorophyll; DM -dodecyl-β-D-maltoside; ECL -enhanced chemiluminescence; HPLC -high performance liquid chromatography; IEC -ion exchange chromatography; GF -gel filtration; LHC I -light harvesting complex associated with Photosystem I; P700 -primary electron donor of photosystem I; SDS -sodium dodecyl sulfate; SQDG -sulfoquinovosyl diacylglycerol; PAGE -polyacrylamide gel electrophoresis; F760 (F730) -fluorescence band with maximal emission at 760 nm (730 nm)

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