The enzyme participates exclusively in sulfur dissimilation. It has lower activity with diethyl sulfide and other short-chain alkyl methyl sulfides. Its activity is stimulated by combined addition of FMN, and, after depletion of cations, of Mg2+ and Fe2+. dimethyl sulfide + O2 + NADH + H+ = methanethiol + formaldehyde + NAD+ + H2O.