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 glu cose or succinate. The activity of the enzyme was maximum with dimethy lnaphthoquinol, 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 en zyme contained 5.3 mumol cytochrome aa3 per gram of protein and neglig ible amounts of cytochrome b and c. The turnover number based on cytoc hrome aa3 was about 10(3) electrons . s-1 at pH 7 and 37-degrees-C. Th e preparation consisted mainly of a M(r) 57000 and a M(r) 36000 polype ptide. The N-terminal amino acid sequence of the latter polypeptide di ffered 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) 36000 polypeptide.