CHARACTERIZATION OF 3-DIMENSIONAL CRYSTALS OF PHOTOSYSTEM II FROM SYNECHOCOCCUS ELONGATUS 
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<sup>1</sup>Zouni A., <sup>1</sup>Fromme P., <sup>2</sup>Schubert W.D., <sup>2</sup>Saenger W., <sup>1</sup>Witt H.T. 
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<sup>1</sup>Max-Volmer-Institut, Technische Universität Berlin, Str. d. 17. Juni 135, D-10623 Berlin <br>
<sup>2</sup>Institut für Kristallographie, Freie Universtität Berlin, Takustr. 6, D-14195 Berlin 
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 Keywords:  photosystem 2, single crystals 
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Highly purified photosystem II complexes were isolated from <i>Synechococcus elongatus</i>. The PS II core complex includes the water-oxidizing center. Crystallization of this protein was performed at 20<sup>o</sup>C in the presence of polyethylene glycol and CaCl<sub>2
</sub>. Single crystals with sizes of 30-400 µm were obtained within 1-2 days. The crystals belong to the orthorhombic space group P222121 or P22212. The unit cell constants are a=134 Å, b=227 Å and c=310 Å. The cell contains four PS II core complexes. Using synchrotron radiation, the crystals diffract X-rays to a resolution of 6 Å at cryogenic temperature. A native data set has been collected.