Structure of ferricytochrome c' from Rhodospirillum rubrum at 6 A resolution

The structure of a ferricytochrome c' extracted from Rhodospirillum rubrum has been determined at 6 A resolution by the X-ray crystallographic method. The crystals, obtained by dialyzing the protein solution against polyethylene glycol 4000, belong to the hexagonal space group P6(1). Two heavy atom derivatives were obtained by soaking the native crystals in K2PtCl6 and CH3HgCl solution. The phases calculated by the multiple isomorphous replacement method gave an overall figure of merit of 0.90 at 6 A resolution. The resulting electron density map showed the molecular boundary clearly, and gave molecular dimensions of 50 X 25 X 30 A for a monomer molecule. From visual examination of this map, the cytochrome c' from Rhodospirillum rubrum has a similar chain-folding pattern to the cytochrome c' from Rhodospirillum molischianum, the structure determination of which has already been carried out.