Identification and Properties of New Flavins in Electron-Transferring Flavoprotein from Peptostreptococcus elsdenii and Pig-Liver Glycolate Oxidase

1 New flavins have been isolated from purified preparations of an electron-transferring flavoprotein (ETF) from Peptostreptococcus elsdenii and glycolate oxidase from pig liver. The structures of these new species have been established as FAD and FMN derivatives of 6-hydroxy-7,8-dimethyl-isoalloxazine, the chemical synthesis of which is described in the accompanying paper by Schöllnhammer and Hemmerich. The chromophores are yellow at pH 5 and green at pH 9 due to an ionization at pK7.1. 2 6-OH-FAD is bound by apo-ETF and its pK is decreased. The complex is reduced by NADH and it couples the oxidation of NADH to the reduction of dichlorophenolindophenol. Unlike the complex of FAD and apo-ETF, 6-OH-FAD ETF does not couple the oxidation of NADH to the reduction of butyryl-CoA dehydrogenase. 3 6-OH-FMN is bound by the FMN-specific protein apoflavodoxin from P. elsdenii and the pK is increased to ∼ 9. This complex is reduced by sodium dithionite and an intermediate, presumed to be the semi-quinone, is formed at half reduction.