Soluble methane mono-oxygenase (sMMO) ofMethylo-coccus capsulatus (Bath) catalyses the O2-dependent and NAD(P)H-dependent oxygenation of methane and numer-ous other substrates. During puri®cation, the sMMO enzyme complex, which comprises three components and has a molecular mass in excess of 300 kDa, becomes inac-tivated because of cleavage of just 12 amino acids from the N-terminus of proteinB, which is the smallest component of sMMOand theonlyonewithout prosthetic groups.
