Analysis of the respiratory chain of the organism is important for understanding the mechanism of aerobic growth in such environments. However, there selleck chemical are only a few reports about the bioenergetics of A. pernix. Many bacteria and archaea have 2 to 6 terminal oxidases in the respiratory chain [3]. The heme-copper oxidase superfamily can be classified into 3 subfamilies (A-, B-, and C-type) on

the basis of the amino acid sequence of subunit I [4, 5]. The group of A-type oxidases includes mitochondrial cytochrome aa 3-type cytochrome c oxidase (complex IV) and many other bacterial oxidases. In contrast, B-type oxidases have been identified mainly from extremophiles, including thermophilic bacteria, such as Geobacillus thermodenitrificans (formerly called Bacillus thermodenitrificans) [6, 7] and Thermus thermophilus [8], and archaea, such as Sulfolobus acidocaldarius [9]. Selleckchem Sapitinib Analysis of the complete genome sequence of A. pernix has shown that it contains A- and B-type heme-copper terminal oxidases (Figure 1). Ishikawa et al. isolated 2 terminal oxidases from A. pernix and designated them as cytochrome ba 3-type (B-type)

and aa 3-type (A-type) cytochrome c oxidases, respectively [10]. Both oxidases have a CuA binding motif, but its substrates have not been identified in the genome sequence. Figure 1 Schematic representation of the respiratory chain of Aeropyrum pernix K1. Genes encoding cytochrome c oxidase and other aminophylline respiratory components in

the bacterium are indicated. ORFs APE_1719.1, APE_1724.1 and APE_1725 encode the cytochrome c 553 complex which was isolated in this study. ORFs APE_0792.1, APE_0793.1 and APE_0795.1, annotated as aoxABC genes, encode an A-type cytochrome c oxidase, and ORFs APE_1623 and APE_1720 encode a B-type cytochrome c oxidase. In the previous study of Ishikawa et al. (2002), these 2 terminal oxidases were designated as cytochrome aa 3- and ba 3-type cytochrome c oxidase, respectively. An extremely haloalkaliphilic archaeon, Natronomonas pharaonis, uses a blue copper protein named halocyanin as a substrate for the terminal oxidase instead of cytochrome c [11]. In S. acidocaldarius, a blue copper protein named sulfocyanin, which is a part of the SoxM supercomplex, is an Buparlisib purchase intermediate in the electron transfer from the bc 1-analogous complex to the terminal oxidase [12]. However, no genes for blue copper proteins homologous to halocyanin or sulfocyanin have been found in the genome of A. pernix. Therefore, although these oxidases can use N, N, N’, N ‘-tetramethyl- p -phenylenediamine (TMPD) and/or bovine cytochrome c as substrates in vitro, the authentic substrate of the two terminal oxidases is not known. In contrast to terminal oxidases, complex III of archaea is not well-known and a canonical bc 1 complex has not been identified in any archaeal genome [13].