LAUSR

The influence of metal removal with a chelating reagent, ethylenediaminetetraacetic acid (EDTA), and metal reconstitution on the activity of particulate methane monooxygenase (pMMO) from Methylosinus trichosporium OB3b toward methane oxidation to methanol was investigated. For this study, a membrane fraction containing pMMO and bacterial cell membrane components was prepared. pMMO activity was assessed with two different reductants, nicotinamide adenine dinucleotide (NADH) and 2,3,5,6-tetramethyl hydroquinone (duroquinol). The partial removal of metal ions with EDTA resulted in the selective inhibition of NADH-driven activity. The NADH-driven activity was restored by exogenous copper ions, but not by other divalent metal cations. Furthermore, both NADH- and duroquinol-driven activities were lost completely by increasing the amount of metal removed. Duroquinol-driven activity of the metal-deficient membrane fraction increased with increasing the amount of copper ions added, while NADH-driven activity increased when more than 5 mol of copper ions per mol of pMMO monomer was added. These results suggest that NADH-driven pMMO activity requires not only the catalytic copper center of pMMO but also copper ions outside the catalytic site.