Dehydrogenase

A dehydrogenase (also called DH or DHase in the literature) is an enzyme belonging to the group of oxidoreductases that oxidizes a substrate by a reduction reaction that removes one or more hydrogens from a substrate to an electron acceptor, usually NAD⁺/NADP⁺ or a flavin coenzyme such as FAD or FMN.

Dehydrogenases are a subclass of the class of enzymes labeled “oxidoreductases.” Oxidoreductases, in general, catalyze oxidation and reduction reactions. Any enzyme that transfers an electron from one molecule to another is considered an oxidoreductase. These enzymes fall into six categories: oxygenases, reductases, peroxidases, oxidases, hydroxylases, and dehydrogenases. Most oxidoreductase enzymes are dehydrogenases, although reductases are also common. Accepted nomenclature for dehydrogenases is "donor dehydrogenase," where the donor is the molecule giving up an electron.

Oxidation-reduction reactions are essential to growth and survival of organisms, as the oxidation of carbons produces energy. Energy-producing reactions can drive forward the synthesis of important energy molecules, such as ATP in glycolysis. For this reason, dehydrogenases have pivotal roles in metabolism.

Dehydrogenases oxidize a substrate by transferring a hydrogen to an electron acceptor, common electron acceptors being NAD⁺ or FAD. This would be considered an oxidation of the substrate, in which the substrate is losing electrons. When considered, the name "dehydrogenase" is a logical moniker for this enzyme, as it facilitates the removal (de-) of a hydrogen (-hydrogen-), by an enzyme (-ase). In contrast, reductases are a subclass of oxidoreductases that catalyze reduction reactions, or a reaction in which a compound is gaining electrons. Dehydrogenase reactions come most commonly in two forms: the transfer of a hydride and release of a proton, and the transfer of two hydrogens.

Typically, a dehydrogenase catalyzed reaction will look like this: AH + B ↔ A⁻ + BH when a hydride is transferred.

A represents the substrate that will be oxidized, while B is the hydride acceptor. Note how when the hydride is transferred from A to B, the A has taken on a positive charge; this is because the enzyme has taken two electrons from the substrate in order to reduce the acceptor to BH.

Acquiring a positive charge is not always the result of a dehydrogenase catalyzed reaction, often the free electrons on the substrate are moved into a double bond. This happens frequently when an alcohol (OH) is the substrate; when the hydrogen is removed the free electrons on the oxygen will be used to create a double bond, as seen in the oxidation of ethanol to acetaldehyde carried out by alcohol dehydrogenase in the image on the right.

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