Copper stress underlies the fundamental change in intracellular location of methane mono-oxygenase in methane-oxidizing organisms: Studies in batch and continuous cultures

Recent results, showing that the ubiquitous methane-utilizing bacteria (methanotrophs) can partially oxidize and, in some cases, extensively metabolize complex organic compounds, call for a reappraisal of their role in the cycling of elements in the biosphere. Possible environmental implications and opportunities for industrial exploitation are discussed.

1. The methane mono-oxygenase from Methylosinus trichosporium OB3b was soluble. The only suitable electron donor was NAD(P)H, neither sodium L-ascorbate nor electrons derived from the oxidation of methanol could substitute for NAD(P)H. Evidence is presented for the existence of an NAD+-linked formaldehyde dehydrogenase. 2. Mono-oxygenase activity was not inhibited by a range of potential inhibitors including potassium cyanide, amytal, carbon monoxide or various metal-chelating agents, although 8-hydroxyquinoline and ethyne were effective in this respect. 3. Although the enzyme preparations were unstable on storage, the crude extract could be resolved into two components by ion-exchange chromatography. Activity could be restored to one of the components on addition of purified components from Methylococcus capsulatus (Bath). 4. Cross-reactivity of mono-oxygenase components and other similarities between the enzymes from M. trichosporium and M. capsulatus are discussed. The properties of the M. trichosporium methane mono-oxygenase reported here are contrasted with the properties of the same enzyme reported by others.