Cytochrome aa3 from the thermoacidophilic archaebacterium Sulfolobus acidocaldarius

Cytochrome aa 3 serves as a terminal oxidase in the thermoacidophilic archaebacterium Sulfolobus acidocaldarius. A procedure for its isolation is described. The purified preparation consists of only one major polypeptide of 38 kDa apparent molecular mass. The enzyme contains two heme α molecules with midpoint potentials of + 220 and + 370 mV, respectively. The copper content is at least 2 Cu/aa 3. It has only negligible capacity to oxidize cytochrome c, but rather serves as an oxidase for reduced caldariella quinone as present in the membrane of Sulfolobus.