Photosynthesis Research

, Volume 72, Issue 3, pp 307-319

First online:

Photosystem I from the unusual cyanobacterium Gloeobacter violaceus

  • D. MangelsAffiliated withMolekulare Pflanzenphysiologie, Universität Bremen
  • , J. KruipAffiliated withBiochemie der Pflanzen, Ruhr-Universität Bochum
  • , S. BerryAffiliated withBiochemie der Pflanzen, Ruhr-Universität Bochum
  • , M. RögnerAffiliated withBiochemie der Pflanzen, Ruhr-Universität Bochum
  • , E.J. BoekemaAffiliated withBiofysische Chemie, Rijksuniversiteit Groningen
  • , F. KoenigAffiliated withMolekulare Pflanzenphysiologie, Universität Bremen Email author 

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Photosystem 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.

antenna system electron microscopy fluorescence light harvesting photosynthesis plasma membrane