Responsible for the initial oxygenation of methane to methanol in methanotrophs. It also catalyzes the monohydroxylation of a variety of unactivated alkenes, alicyclic, aromatic and heterocyclic compounds. The component C is the iron-sulfur flavoprotein of sMMO. H(+) + methane + NADH + O2 = H2O + methanol + NAD(+) H(+) + methane + NADPH + O2 = H2O + methanol + NADP(+) Binds 1 [2Fe-2S] cluster. The soluble methane monooxygenase (sMMO) consists of four components A/MMOH (composed of alpha/MmoX, beta/MmoY and gamma/MmoZ), B/MMOB (MmoB), C/MMOR (MmoC) and D/MMOD (MmoD).