Preparation and X-ray structures of metal-free, dicobalt and dimanganese forms of soluble methane monooxygenase hydroxylase from Methylococcus capsulatus (Bath)

A three-component soluble methane monooxygenase (sMMO) enzyme system catalyzes the hydroxylation of methane to methanol at a carboxylate-bridged diiron center housed in the a-subunit of the hydroxylase (MMOH). Catalysis is facilitated by the presence of a regulatory protein (MMOB) and inhibited by MMOD, a protein of unknown function encoded in the sMMO operon. Both MMOB and MMOD are presumed to bind to the same region of the MMOH a-subunit. A colorimetric method for monitoring removal of Fe(II) from MMOH was developed using 1,10-phenanthroline and yields apo MMOH wit