Identification of cytochrome c oxidase in the alkaliphilic, obligately chemolithoautotrophic, sulfur-oxidizing bacterium 'Thioacalomicrobium aerophilum' strain AL 3

Cytochrome c oxidase from the novel alkaliphilic autotrophic sulfur bacterium 'Thioalcalomicrobium aerophilum' strain AL 3 was isolated and purified 87-fold. Spectroscopic analysis revealed the presence of both c- and b-type hemes as well as copper in a ratio of 3:2:1. The purified enzyme consists of three subunits with apparent molecular masses of 41, 34 and 32 kDa. The two small subunits contain covalently bound heme c. With TMPD as a substrate the pH optimum was determined to be pH 8.0. In the presence of monovalent cations the specific activity of the purified oxidase increased significantly. The enzyme was not able to oxidize external cytochrome c, but accepted electron from its native electron donor. The latter was separated from the other membrane cytochromes during anion-exchange chromatography and was identified as a high potential cytochrome c(551). Overall the data indicate that the cytochrome c oxidase from this alkaliphilic autotrophic bacterium belongs to the heme-copper oxidase superfamily; regarding its subunit composition and content of prosthetic groups, the enzyme is similar in many aspects to the cbb(3)-type cytochrome c oxidases described for several neutrophilic bacteria, including anaerobic phototrophic and aerobic sulfur-oxidizing bacteria. (C) 1999 Published by Elsevier Science B.V. All rights reserved.