NADH dehydrogenase catalyzes electron transport from NADH to ubiquinone. It contains a large number of subunits, fourteen of which are conserved across species. It contains a transmembrane portion (with 7 conserved subunits), which carries electrons to ubiquinone, and a soluble portion (with 7 conserved subunits) which accepts electrons from NADH. These electrons are transferred to a
. They are then sequentially transferred to a
The model shown only includes a soluble moiety of the complex. Reduction of ubiquinone to ubiquinol by the electrons carried by the Fe-S clusters cannot be shown, since it occurs in the membrane portion of the complex, of which the three-dimensional structure is still unknown.