Oxidoreductases

Oxidoreductases are enzymes that catalyze oxidation-reduction (redox) reactions in which electrons are transferred between two substrates. They form EC class 1 of the Enzyme Commission nomenclature. In a typical redox pair, one molecule is oxidized and another is reduced. Many oxidoreductases rely on cofactors such as nicotinamide adenine dinucleotide (NAD+) or NAD phosphate (NADP+), flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN), and various metal cofactors that participate in electron transfer.

Subclasses include dehydrogenases, which commonly transfer hydride ions to NAD+/NADP+ or related carriers; oxidases, which transfer electrons to molecular oxygen and often produce water or hydrogen peroxide; reductases, which donate electrons to reduce substrates; and oxygenases, which incorporate oxygen atoms into substrates (monooxygenases and dioxygenases). Other related enzymes include peroxidases and hydroxylases. Notable examples are lactate dehydrogenase (NAD+-dependent), alcohol dehydrogenase, succinate dehydrogenase, and cytochrome c oxidase.

Oxidoreductases typically require cofactors such as NAD+/NADH, NADP+/NADPH, FAD/FADH2, FMN/FMNH2, iron-sulfur clusters, heme, or molybdenum cofactors to shuttle electrons. They are found throughout cellular compartments, including mitochondria, chloroplasts, cytosol, and bacterial cells, and they participate in energy production, biosynthetic redox reactions, detoxification, and maintenance of redox balance. Their activity is often regulated by cellular redox state and availability of acceptors.

Measurement of oxidoreductase activity commonly relies on monitoring changes in absorbance of cofactors such as NADH or NADPH, or by coupling reactions to detectable readouts. Dysfunction or imbalance in oxidoreductases can contribute to metabolic disorders and oxidative stress, illustrating their essential role in health and disease.