PARENT SESSION
Posters P5A Type II reaction centres : Structure. Abstracts (289-312)

Biochemical and functional analysis of Photosystem II crystals from Thermosynechococcus elongatus diffracting to 3.2 . Athina Zouni^*,1, Jan Kern¹, Joachim Frank¹, Joachim Behlke², Peter Franke³, Klaus-D. Irrgang¹, ¹ Max-Volmer-Laboratory for Biophysical Chemistry, Berlin, Germany² Max-Dellbrück-Centre for Molecular Medicine, Berlin-Buch, Berlin, Germany³ Institute for Biochemistry, Berlin, Germany

ABSTRACT- Cells of the thermophilic cyanobacterium Thermosynechococcus elongatus were cultivated in a new type of photobioreactor allowing us to optimize the biomass yield and also the stoichiometry of Photosystem I / Photosystem II (PSI)/(PSII). Dimeric oxygen evolving PS II was solubilized from thylakoid membranes with n - beta- dodecylmaltoside and purified using anion exchange chromatography. The molecular composition of the detergent-solubilized PS II was analysed as follows: a) the protein subunit composition by SDS/urea/PAGE, MALDI-TOF-MS, immunological screening and absorbance difference spectroscopy b) chromophores by reversed-phase HPLC, TLC and absorbance spectroscopy, c) lipid and detergent molecules by 2d-TLC and gas chromatography. The holocomplex consists of 19 ± 1 protein subunits, 35-36 Chl a , 2 Pheo a, 1.4-2.1 Plastoquinone 9, 9-11 carotenoids and about 10 lipid molecules per monomer. The manganese content was determined by atom absorption spectroscopy (4 ± 1 per monomer). The dimeric holocomplex reveals a molecular mass of 756 ± 18 kDa and is functionally fully active (45 ±10 Chla/oxygen evolving centre; 3500-4000 micromol O₂/mg Chl x h). On the basis of these samples crystals of significantly improved quality were recently obtained leading to a 3D structure at 3.2 resolution.

KEY WORDS: Photosystem II, biochemical and functional analysis, Thermosynechococcus elongatus, water splitting enzyme