Unformatted text preview: n transfer from N-2 to ubiquinone on the
membrane arm forms QH2, which diffuses into the lipid bilayer. This
electron transfer also drives the expulsion from the matrix of four protons per pair of electrons. The detailed mechanism that couples electron and proton transfer in Complex I is not yet known, but probably
involves a Q cycle similar to that in Complex III in which QH2 participates twice per electron pair (see Fig. 19–12). Proton ﬂux produces an
electrochemical potential across the inner mitochondrial membrane (N
side negative, P side positive), which conserves some of the energy released by the electron-transfer reactions. T...
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