dimethylamine + H(+) + H2O + oxidized [electron-transfer flavoprotein] = formaldehyde + methylamine + reduced [electron-transfer flavoprotein] Binds 1 FMN covalently per subunit. Binds 1 [4Fe-4S] cluster per subunit. In the N-terminal section; belongs to the NADH:flavin oxidoreductase/NADH oxidase family.