CO oxidoreductase from Streptomyces strain G26 is a molybdenum hydroxylase

CO oxidoreductase was purified to 95% homogeneity from crude mycelial extracts of Streptomyces G26. The purified preparation has a specific activity of 25.7 units/mg, a 13-fold improvement on crude soluble mycelial extracts. The native enzyme (Mr 282,000) is composed of non-identical subunits of Mr 110,000 and 33,000. It is a molybdenum hydroxylase containing 1.6 mol of FAD, 7.3 mol of Fe, 8.3 mol of acid-labile sulphide and 1.3 mol of Mo per mol of enzyme. Purified CO oxidoreductase catalyses the reduction of benzyl viologen, confirming the previously reported ability of this enzyme to interact with low-potential acceptors. Cytochrome c reduction cannot be accounted for entirely by non-enzymic reduction by superoxide radicals. NAD+ and NADP+ are not reduced, nor is clostridial ferredoxin.