The menaquinol oxidase of Bacillus subtilis W23

The quinol oxidase appears to be mainly responsible for the oxidation of the 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 mumol cytochrome aa3 per gram of protein and negligible amounts of cytochrome b and c. The turnover number based on cytochrome aa3 was about 10(3) electrons.s-1 at pH 7 and 37 degrees C. The preparation consisted mainly of a M(r) 57,000 and a M(r) 36,000 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 M(r) 36,000 polypeptide.