Measurement of the oxidation-reduction potentials for one-electron and two-electron reduction of electron-transfer flavoprotein from pig liver

Abstract

Potentiometric titrations of pig liver electron-transfer flavoprotein (ETF) were performed at pH 7.5 and 4.degree. C, both in the reductive and oxidative directions. Reduction of ETF to the hydroquinone form required a total of 2 reducing equivalents/mol of ETF with the formation of sub-stoichiometric amounts of anionic semiquinone as an intermediate. The oxidation-reduction potentials for the 2, 1-electron couples, oxidized ETF/ETF semiquinone and ETF semiquinone/fully reduced ETF, are + 4mV and -50mV, respectively. The overall midpoint potential for the 2-electron couple (oxidized ETF/fully reduced ETF) is -23mV.