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

Membranes of the extremely thermoacidophilic archaeon Desulfurolobus a mbivalens grown under aerobic conditions contain a quinol oxidase of t he cytochrome aa(3)-type as the most prominent hemoprotein. The partia lly purified enzyme consists of three polypeptide subunits with appare nt molecular masses of 40, 27 and 20 kDa and contains two heme A molec ules 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-sp in and a high-spin heme species. Redox titrations of the solubilized e nzyme show the presence of two reduction processes, with apparent pote ntials of + 235 and + 330 mV. The enzyme cannot oxidize reduced cytoch rome c, but rather serves as an oxidase of caldariella quinone. Due to their very simple composition, D. ambivalens cells appear as a promis ing candidate to study structure-function relationships of cytochrome aa(3) in the integral membrane state.