ABSTRACT
Electron-transferring flavoprotein (ETF) was first identified by Crane and Beinert as a yellow fluorescent component required to mediate the transfer of reducing equivalents from mammalian fatty acyl-CoA dehydrogenases to various electron acceptors. ETF from mammalian sources are heterodimers with molecular weights of about 33 and 28 kDa for a- and B-subunits. In addition to mammalian ETFs, a number of electron-transferring flavoproteins or ETF-like proteins have been isolated from bacterial sources. Dithionite titrations of mammalian ETFs yield the red anionic flavosemiquinone as evident by the appearance of a species with a strong absorption at 375 nm. Rapid reaction studies of the interflavin electron transfer reactions between octanoyl-CoA reduced medium-chain acyl-CoA dehydrogenase and oxidized ETF revealed first the appearance and then the slower decay of the red ETF radicai. ETF has been isolated from two strains of methylotrophic bacteria: W3A1 and Methylophilus methylotrophus.
