Abstract
Membranes of the extremely thermoacidophilic archaeon Desulfurolobus ambivalens grown under aerobic conditions contain a quinol oxidase of the cytochrome aa3-type as the most prominent hemoprotein. The partially purified enzyme consists of three polypeptide subunits with apparent molecular masses of 40, 27 and 20 kDa and contains two heme A molecules and one copper atom. CO difference spectra suggest one heme to be a heme a3-centre. The EPR spectra indicate the presence of a low-spin and a high-spin heme species. Redox titrations of the solubilized enzyme show the presence of two reduction processes, with apparent potentials of + 235 and + 330 mV. The enzyme cannot oxidize reduced cytochrome c, but rather serves as an oxidase of caldariella quinone. Due to their very simple composition, D. ambivalens cell appear as a promising candidate to study Structure-function relationships of cytochrome aa3 in the integral membrane state.
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