The Structure of Cytochrome a from Desulfovibrio vulgaris o

The structure of tetraheme cytochrome cs isolated from Desulfovibrio vulgaris Miyazaki has been determined at 2.5 A resolution by an X-ray diffraction method. Protein phases were computed by the multiple isomorphous replacement method using the native and four heavy atom derivatives, anomalous scattering measure-ments of the latter being considered. The mean figure of merit was 0.77. Four heme groups are exposed on the surface of the molecule. There are some short helical segments in the polypeptide chain, and hair-pin turns are often observed at glycine and alanine residues. Cytochrome c, (7, 2), an electron carrier for hydrogenase [EC 1.12.2.1] (5-5) in sulfate-reducing bacteria has an unusually low redox potential, which seems to be attributed to the fact that it has four heme groups (5). Some kinds of cyto-chrome c3 have been isolated and characterized from various strains of sulfate-reducing bacteria. One of them, cytochrome ct from Desulfovibrio desulfuricans Norway, has been investigated by an X-ray diffraction method, and the preliminary results have been reported (7)