Electron transfer flavoprotein beta subunit lysine methyltransferase (ETFBKMT, METTL20) specifically methylates Lys-200 and Lys-203 of Electron transfer flavoprotein beta (ETFB) ) (Rhein et al 2014, Malecki et al. 2015). ETF shuttles electrons between several FAD-containing dehydrogenases present in the mitochondrial matrix and the membrane-bound ETF:quinone oxidoreductase (Ramsay et al. 1987). ETFB is proposed to contain 'recognition loop' at residues 191–200, responsible for interaction with the dehydrogenases (Toogood et al. 2004). Methylation of ETF impairs its ability to extract electrons from two acyl-CoA dehydrogenases, MCAD and GCDH, suggesting a functional role for ETFBKMT-mediated methylation of ETFB (Malecki et al. 2015).