The proton-pumping NADH:ubiquinone oxidoreductase (complex I) couples the transfer of electrons from NADH to ubiquinone with the translocation of protons across the membrane. Electron transfer is accomplished by flavin mononucleotide (FMN) and a series of iron-sulfur (Fe/S) clusters. A novel mechanism has been proposed wherein the electron transfer reaction induces conformational changes that subsequently lead to the translocation of protons. Redox-induced Fourier transform infrared difference spectra have been obtained, showing strong conformational changes in the amide I region. The amplitude of the signal is pH dependent, as expected for an energy coupling step in the enzymes reaction. Furthermore, pH-dependent protonation events and quinone binding were detected.
Copyright 2004 Wiley Periodicals, Inc. Biopolymers, 2004