PROJECTION MAP OF CYTOCHROME B(6)F COMPLEX AT 8 ANGSTROM RESOLUTION

The structure of the cytochrome b(6)f complex has been investigated by electron microscopy and image analysis of thin three-dimensional crys tals. Electron micrographs of negatively stained specimens were record ed and showed optical diffraction peaks to 10 Angstrom resolution. A p rojection map was calculated at 8 Angstrom resolution and showed the p resence of cytochrome b(6)f dimers. The extramembrane part of each mon omer featured a C shape, with mean external diameter similar to of 53 Angstrom and an internal groove similar to 14 Angstrom long and simila r to 9 Angstrom wide. Within each monomer, strong features were clearl y resolved and tentatively attributed to some of the subunits of the c ytochrome b(6)f complex, The data are consistent with the Rieske iron- sulfur protein lying close to the monomer-monomer interface and the he me-bearing domain of cytochrome f far from it.