enzymology Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

, a monodehydroascorbate reductase (MDAR) () is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

that

catalyzes Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

the

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

:NADH + H⁺ + 2 monodehydroascorbate

\rightleftharpoons

NAD⁺ + 2 ascorbate The 3 substrates of this enzyme are

NADH Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an aden ...

, H⁺, and monodehydroascorbate, whereas its two

products Product may refer to: Business * Product (business), an item that serves as a solution to a specific consumer problem. * Product (project management), a deliverable or set of deliverables that contribute to a business solution Mathematics * Produ ...

are NAD⁺ and

ascorbate Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) and ...

. This enzyme belongs to the family of

oxidoreductase In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor. This group of enzymes usually ut ...

s, specifically those acting on NADH or NADPH, with a quinone or similar compound as an acceptor. The

systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivial ...

of this enzyme class is NADH: monodehydroascorbate oxidoreductase. Other names in common use include NADH: semidehydroascorbic acid oxidoreductase, MDHA, semidehydroascorbate reductase, AFR, AFR-reductase, ascorbic free radical reductase, ascorbate free radical reductase, SOR, MDAsA reductase (NADPH), SDA reductase, NADH: ascorbate radical oxidoreductase, NADH-semidehydroascorbate oxidoreductase, ascorbate free-radical reductase, NADH: AFR oxidoreductase, and monodehydroascorbate reductase (NADH2). This enzyme participates in

and aldarate metabolism. In plants, the monodehydroascorbate reductase (MDAR) is an enzymatic component of the

glutathione-ascorbate cycle The ascorbate-glutathione cycle, sometimes Foyer-Halliwell- Asada pathway, is a metabolic pathway that detoxifies hydrogen peroxide (H2O2), a reactive oxygen species that is produced as a waste product in metabolism. The cycle involves the antiox ...

that is one of the major

antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...

systems of plant cells for the protection against the damages produced by

reactive oxygen species In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. The reduction of molecular oxygen () p ...

(ROS). The MDAR activity has been described in several cell compartments, such as

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells (intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...

mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...

, glyoxysomes, and leaf

peroxisomes A peroxisome () is a membrane-bound organelle, a type of microbody, found in the cytoplasm of virtually all eukaryotic cells. Peroxisomes are oxidative organelles. Frequently, molecular oxygen serves as a co-substrate, from which hydrogen pero ...

References

* EC 1.6.5 NADPH-dependent enzymes NADH-dependent enzymes Enzymes of unknown structure {{1.6-enzyme-stub