NADH dehydrogenase (), Complex I of the mitochondrial electron transfer chain, catalyzes the transfer of electrons from NADH to coenzyme Q (CoQ). It is also known as the NADH:Ubiquinone oxidoreductase.

2NADH + CoQ + 2H⁺ → 2NAD⁺ + CoQH₂

In the process, the complex also translocates protons across the inner membrane, helping to build the electrochemical potential used to produce ATP.

It is the largest of the respiratory complexes, the mammalian enzyme containing 42 separate polypeptide chains. Of particular functional importance are the flavin prosthetic group and eight iron-sulfur clusters. Of the 42 subunits, seven are encoded by the mitochondrial genome.

Defects in the subunits of Complex I are associated with various mitochondrial diseases, including Leigh syndrome and Parkinson's disease.

Piericidin and rotenone, an antibiotic inhibits electron flow from the iron sulfur center N2 to the ubiquinone molecule.

More information can be found on the Complex I home page.

Cellular respiration | EC 1.6.5