The menaquinol oxidase of Bacillus subtilis W23
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The quinol oxidase appears to be mainly responsible for the oxidation of bacterial MKH2 in Bacillus subtilis W23 growing with either glucose or succinate. The activity of the enzyme was maximum with dimethylnaphthoquinol, a water-soluble analogue of the bacterial menaquinol. Menadiol or duroquinol were less actively respired, and naphthoquinol was not oxidized at all. After fourtyfold purification the isolated enzyme contained 5.3 μmol cytochrome aa3 per gram of protein and negligible amounts of cytochrome b and c. The turnover number based on cytochrome aa3 was about 103 electrons · s-1 at pH 7 and 37°C. The preparation consisted mainly of a Mr 57000 and a Mr 36000 polypeptide. The N-terminal amino acid sequence of the latter polypeptide differed from that predicted by the qoxA gene of B. subtilis strain 168 (Santana et al. 1992), in that asp-14 predicted by qoxA was missing in the Mr 36000 polypeptide.
Key wordsBacillus subtilis Electron transport Quinol oxidase Respiration Menaquinone
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