A dehydrogenase (DH or DHase) is an enzyme that is part of the oxidoreductases group. The enzyme oxidizes a substrate by reducing an electron acceptor, which us usually NAD+/NADP+ or a flavin coenzyme such as FAD or FMN. This type of enzyme also catalyzes the reverse reaction. For example, alcohol dehydrogenase both oxidizes ethanol to acetaldehyde in animals and produces ethanol from acetaldehyde in yeast.
The dehydrogenase subclass of enzymes is part of the oxidoreductases group. Oxidoreductases mostly catalyze oxidation and reduction reactions and have six different categories, of which dehydrogenases is one. The others are oxygenases, reductases, peroxidases, oxidases and hydroxylases. However, most oxidoreductases are actually dehydrogenases. Oxidation-reduction reactions play a vital role in growth for organisms. When the oxidation of organic molecules takes place, it produces energy and contributes to the synthesis of energy molecules. Dehydrogenases play an important part in metabolism.
Dehydrogenases transfer hydrogen to an electron acceptor to oxidize a substrate. The substrate can lose hydrogen atoms or might gain an oxygen atom. There are two common forms of dehydrogenase reactions, which are the transfer of a hydride and loss of a proton, as well as the transfer of two hydrogens.
In addition to acquiring a positive charge, a substrate can also lose a proton, which can leave free electrons on the substrate. These free electrons form a double bond. One example of when this happens is when the substrate is an alcohol, such as in the oxidation of ethanol to acetaldehyde. It is also possible for a water molecule to enter and contribute a hydroxide ion to the substrate and proto to the environment. This means that the substrate has an extra oxygen atom. An example of this is in the oxidation of acetaldehyde to acetic acid, which occurs when ethanol is metabolizing and when vinegar is made.
The different subclasses of oxidoreductases that catalyze oxidation reactions are differentiated by their electron acceptors. Dehydrogenase and oxidase are both easy to distinguish from the other subclasses thanks to their electron receptors. Dehydrogenase enzymes move electrons from the substrate to an electron carrier. This electron carrier differs depending on the reaction. Some common acceptors used by dehydrogenases include NAD+, FAD, and NADP+. This process involves the reduction of electron carriers, which are considered to oxidize the substrate. Electron carriers are often called redox cofactors, as a type of coenzyme.
One example of how a dehydrogenase has an important function is aldehyde dehydrogenases (ALDH). These NAD+-dependent enzymes remove aldehydes from the body to prevent their toxic effect. Aldehydes are a by-product of many processes and are also found in the environment, from various industrial processes. If they accumulate in the brain and pericardium, they can have adverse health effects. Acetaldehyde is an intermediate in the metabolism of ethanol. Its buildup can cause hangover symptoms, and people with a deficiency of acetaldehyde dehydrogenases have bad reactions to alcohol.