Bacillus subtilis expresses two kinds of haem‐A‐containing terminal oxidases

Abstract

The expression of two different aa3‐type cytochrome oxidases is demonstrated in Bacillus subtilis. One of them (denoted caa3‐605), was predicted by DNA‐sequencing of Bacillus cytochrome oxidase genes, but has not been found previously. It contains covalently bound haem C in subunit II and is very similar to the enzyme previously described in the thermophilic bacterium PS3. The other oxidase (denoted aa3‐600) deviates from most known oxidases of aa3 type, and is probably identical with the oxidase described by de Vrij et al. [de Vrij, W., Azzi, A. & Konings, W. N. (1983) Eur. J. Biochem. 131, 97–103]. It shows no immunological cross‐reactivity to the PS3 enzyme and differs from this spectroscopically; it contains no CuA and does not oxidise cytochrome c despite of its haem‐A chromophores. It catalyses oxidation of quinols, which is proposed to be its physiological function.

EPR studies of cytochrome aa3 from Sulfolobus acidocaldarius

“…The EPR spectrum of the extensively dialyzed enzyme, which essentially retained its activity and contains only one copper atom/protein molecule, does not show any copper EPR signal. This observation proves the absence of a center analogous to CuA of mammalian cytochrome 4u3, as has been also shown for the E. coli cytochrome bo [25] and the B. subtilis cytochrome aa3-600 [23]. This type of copper center in cytochrome c oxidases is a ligand of subunit I1 of the terminal oxidase complexes.…”

“…Cytochrome uu3 generally oxidizes reduced cytochrome c, whereas cytochrome bo functions as an ubiquinol oxidase. Meanwhile, an alternative terminal oxidase from Bacillus subtilis, cytochrome aa3-600, could also be shown to act as an aa3-type quinol oxidase [23]. Thus, the capability of cytochrome aa3 to use quinols as substrates seems to be a common feature in the eubacterial and archaebacterial urkingdoms.…”

“…This implies that all physiological functions in terminal electron transport are unified in the single-subunit cytochrome uu3 from Sulfolobus. Furthermore, the absence of CuA seems to be characteristic for quinol oxidases as also shown for E. coli cytochrome bo [25] and B. subtilis cytochrome au3-600 [23], while its presence is a prerequisite for cytochrome c to replace quinol as an electron donor.…”

A Cytochrome bb′-type Quinol Oxidase inBacillus subtilis Strain 168

“…It is encoded by the qoxABCD operon (13) and accordingly contains four subunits (polypeptides QoxA, -B, -C, and -D) (14). The caa 3 -type COX is expressed during growth on nonfermentable substrates such as succinate (7). It is also a typical proton-pumping hemecopper oxidase and is encoded by the ctaCDEF genes (15).…”

“…The major one is an aa 3 -type QOX (7)(8)(9) that is expressed in rich media at all stages of growth. This enzyme belongs to the heme-copper superfamily (e.g.…”