Dehydrogenases

Dehydrogenases are a subclass of oxidoreductase enzymes that catalyze oxidation-reduction reactions in which hydrogen atoms are removed from a substrate and transferred to an electron acceptor. The primary electron acceptors are nicotinamide adenine dinucleotide (NAD+) and NADP+, forming NADH or NADPH, but some dehydrogenases use flavin cofactors such as FAD or FMN or metal ions.

They play central roles in cellular metabolism, including glycolysis, the citric acid cycle, gluconeogenesis, and respiration, as well as in fermentation and biosynthesis. The direction of the reaction depends on substrate and product concentrations and the redox state of the cell.

Examples include lactate dehydrogenase (lactate to pyruvate with NADH to NAD+), alcohol dehydrogenase (ethanol to acetaldehyde), glyceraldehyde-3-phosphate dehydrogenase (GAPDH in glycolysis with NAD+), and malate dehydrogenase (malate to oxaloacetate in the TCA cycle). Some enzymes like succinate dehydrogenase also participate in electron transport and use FAD.

Enzymes are classified as EC 1.x.x.x under oxidoreductases. Dehydrogenases are often named for their substrates and cofactors, but the term also overlaps with reductases and other oxidative enzymes. They can be cytosolic or mitochondrial and may require metal cofactors.

In biotechnology and medicine, dehydrogenases are used as biocatalysts and biosensors; abnormal dehydrogenase activity can indicate tissue damage or metabolic disorders.