High Quality Content by WIKIPEDIA articles! NADH dehydrogenase (EC 1.6.5.3) (also referred to as NADH:ubiquinone reductase or Complex I) is an enzyme located in the inner mitochondrial membrane that catalyzes the transfer of electrons from NADH to coenzyme Q (CoQ). It is one of the "entry enzymes" of oxidative phosphorylation in the mitochondria.