This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Two proteins, Rieske iron-sulfur and cytochrome ba(3), from the thermophilic eubacterium, Thermus thermophilus, involved in respiration are proposed to be studied at high resolution and in multiple oxidation states and pH levels. The oxidized Rieske protein has been solved at pH 8.5 yielding the structure of the partially protonated form, which gives insight into the mechanism of H(+) translocation. However, the ultra-high resolution (<1 [unreadable]) structure at pH 8.5, the low pH and reduced state protonated structures at high resolution are also vital to define mechanistic features. Novel ba(3) structures of the cyano complex and the reduced, carbonylated form, at high resolution, should yield additional information regarding this protein's function.