PRELIMINARY-X-RAY CRYSTALLOGRAPHIC STUDIES OF PHOTOSYNTHETIC REACTION-CENTER FROM A THERMOPHILIC SULFUR BACTERIUM, CHROMATIUM-TEPIDUM

A membrane protein complex, photosynthetic reaction center purified fr om the thermophilic purple sulfur bacterium, Chromatium tepidum has be en crystallized from a phosphate buffer containing a detergent, n-octy l-beta-D-glucopyranoside and a precipitant, polyethylene glycol 4000. The crystals diffracted X-rays beyond 3 Angstrom resolution with synch rotron radiation and are suitable for high-resolution X-ray crystallog raphic studies. The crystals belong to the orthorhombic space group P2 (1)2(1)2(1) with unit-cell dimensions of a = 136 Angstrom, b = 197 Ang strom, and c = 82 Angstrom. Assuming that they contain one reaction ce nter complex in the asymmetric unit, V-M was calculated to be 4.3 Angs trom(3)/Da, which agrees with the values obtained in the membrane prot ein complexes.