In biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...

, an oxidoreductase is an enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 that catalyzes the transfer of electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s from one molecule (the reductant
Reducing agent
A reducing agent is the element or compound in a reduction-oxidation reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized"...

, also called the hydrogen or electron donor
Electron donor
An electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process....

) to another (the oxidant, also called the hydrogen or electron acceptor). This group of enzymes usually utilizes NADP or NAD
NAD may refer to:* No abnormality detected, a medical status description* No apparent distress, a status description in childbirth* NAD Electronics, a Canadian audio equipment manufacturer...

 as cofactor
Cofactor (biochemistry)
A cofactor is a non-protein chemical compound that is bound to a protein and is required for the protein's biological activity. These proteins are commonly enzymes, and cofactors can be considered "helper molecules" that assist in biochemical transformations....



For example, an enzyme that catalyzed this reaction would be an oxidoreductase:
A + B → A + B

In this example, A is the reductant (electron donor) and B is the oxidant (electron acceptor).

In biochemical reactions, the redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 reactions are sometimes more difficult to see, such as this reaction from glycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...

Pi + glyceraldehyde-3-phosphate + NAD+ → NADH + H+ + 1,3-bisphosphoglycerate

In this reaction, NAD+ is the oxidant (electron acceptor), and glyceraldehyde-3-phosphate is the reductant (electron donor).


Proper names of oxidoreductases are formed as "donor:acceptor oxidoreductase"; however, other names are much more common. The common name is "donor dehydrogenase
A dehydrogenase is an enzyme that oxidises a substrate by a reduction reaction that transfers one or more hydrides to an electron acceptor, usually NAD+/NADP+ or a flavin coenzyme such as FAD or FMN.-Examples:...

" when possible, such as glyceraldehyde-3-phosphate dehydrogenase for the second reaction above. Common names are also sometimes formed as "acceptor reductase", such as NAD+ reductase. "Donor oxidase
An oxidase is any enzyme that catalyzes an oxidation-reduction reaction involving molecular oxygen as the electron acceptor. In these reactions, oxygen is reduced to water or hydrogen peroxide ....

" is a special case where O
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

2 is the acceptor.


Oxidoreductases are classified as EC 1 in the EC number
EC number
The Enzyme Commission number is a numerical classification scheme for enzymes, based on the chemical reactions they catalyze....

 classification of enzymes. Oxidoreductases can be further classified into 22 subclasses:
  • EC 1.1 includes oxidoreductases that act on the CH-OH group of donors (alcohol oxidoreductases
    Alcohol oxidoreductases
    Alcohol oxidoreductases are oxidoreductase enzymes that act upon an alcohol functional group.They are classified under "1.1" in the EC number numbering system.-External links:...

  • EC 1.2 includes oxidoreductases that act on the aldehyde
    An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....

     or oxo group of donors
  • EC 1.3 includes oxidoreductases that act on the CH-CH group of donors (CH-CH oxidoreductases
    CH-CH oxidoreductases
    CH–CH oxidoreductases are oxidoreductase enzymes that convert single bonds and double bonds between two carbon atoms. They are classified under EC number 1.3.One example is 5-alpha reductase:...

  • EC 1.4 includes oxidoreductases that act on the CH-NH2 group of donors (Amino acid oxidoreductases
    Amino acid oxidoreductases
    Amino acid oxidoreductases are oxidoreductases, a type of enzyme, that act upon amino acids.They constitute the majority of enzymes classified under EC number 1.4, with most of the remainder being monoamine oxidases.Examples include:...

    , Monoamine oxidase
    Monoamine oxidase
    L-Monoamine oxidases are a family of enzymes that catalyze the oxidation of monoamines. They are found bound to the outer membrane of mitochondria in most cell types in the body. The enzyme was originally discovered by Mary Bernheim in the liver and was named tyramine oxidase...

  • EC 1.5 includes oxidoreductases that act on CH-NH group of donors
  • EC 1.6 includes oxidoreductases that act on NADH or NADPH
  • EC 1.7 includes oxidoreductases that act on other nitrogenous compounds as donors
  • EC 1.8 includes oxidoreductases that act on a sulfur
    Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

     group of donors
  • EC 1.9 includes oxidoreductases that act on a heme
    A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...

     group of donors
  • EC 1.10 includes oxidoreductases that act on diphenol
    Benzenediols or dihydroxybenzenes are organic chemical compounds in which two hydroxyl groups are substituted onto a benzene ring. These aromatic compounds are classed as phenols, and more specifically as polyphenols...

    s and related substances as donors
  • EC 1.11 includes oxidoreductases that act on peroxide
    A peroxide is a compound containing an oxygen–oxygen single bond or the peroxide anion .The O−O group is called the peroxide group or peroxo group. In contrast to oxide ions, the oxygen atoms in the peroxide ion have an oxidation state of −1.The simplest stable peroxide is hydrogen peroxide...

     as an acceptor (peroxidase
    Peroxidases are a large family of enzymes that typically catalyze a reaction of the form:For many of these enzymes the optimal substrate is hydrogen peroxide, but others are more active with organic hydroperoxides such as lipid peroxides...

  • EC 1.12 includes oxidoreductases that act on hydrogen as donors
  • EC 1.13 includes oxidoreductases that act on single donors with incorporation of molecular oxygen (oxygenase
    An oxygenase is any enzyme that oxidizes a substrate by transferring the oxygen from molecular oxygen O2 to it. The oxygenases form a class of oxidoreductases; their EC number is EC 1.13 or EC 1.14....

  • EC 1.14 includes oxidoreductases that act on paired donors with incorporation of molecular oxygen
  • EC 1.15 includes oxidoreductases that act on superoxide
    A superoxide, also known by the obsolete name hyperoxide, is a compound that possesses the superoxide anion with the chemical formula O2−. The systematic name of the anion is dioxide. It is important as the product of the one-electron reduction of dioxygen O2, which occurs widely in nature...

     radicals as acceptors
  • EC 1.16 includes oxidoreductases that oxidize metal ions
  • EC 1.17 includes oxidoreductases that act on CH or CH2 groups
  • EC 1.18 includes oxidoreductases that act on iron-sulfur proteins as donors
  • EC 1.19 includes oxidoreductases that act on reduced flavodoxin
    Flavodoxins are electron-transfer proteins. Flavodoxin is a bacterial protein that includes flavin mononucleotide. The structure of flavodoxin is characterized by a five-stranded parallel beta sheet, surrounded by alpha helices at either side of the sheet. They have been isolated from prokaryotes,...

     as a donor
  • EC 1.20 includes oxidoreductases that act on phosphorus
    Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

     or arsenic
    Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...

     in donors
  • EC 1.21 includes oxidoreductases that act on X-H and Y-H to form an X-Y bond
  • EC 1.97 includes other oxidoreductases

External links

  • EC 1 Introduction from the Department of Chemistry at Queen Mary, University of London
    Queen Mary, University of London
    Queen Mary, University of London is a public research university located in London, United Kingdom and a constituent college of the federal University of London...

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