A CYTOCHROME AA(3)-TYPE QUINOL OXIDASE FROM DESULFUROLOBUS AMBIVALENS, THE MOST ACIDOPHILIC ARCHAEON

Membranes of the extremely thermoacidophilic archaeon Desulfurolobus ambivalens grown under aerobic conditions contain a quinol oxidase of the cytochrome aa(3)-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 a(3)-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 cells appear as a promising candidate to study structure-function relationships of cytochrome aa(3) in the integral membrane state.