The immediate objective of the proposed research is to further refine the models of iron-sulfur proteins which have already been solved (a bacterial ferredoxin, rubredoxin from D. vulgaris) and to determine the structures of additional iron-sulfur proteins as well as other electron transport proteins. An additional objective is to correlate the properties of these proteins with a view to eventually understanding how they function. The methods used are those of protein crystallography: preparation and purification of the protein, growth of crystals, search for heavy atom derivatives, collecting diffraction data from native and derivative crystals, data processing, solution of the structure, and refinement of the model including display.