In molecular biology, a dioxygenase is an enzyme

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...

 which catalyses the incorporation of both atom

Atom

The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...

s of molecular oxygen

Oxygen

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...

 into substrates

Substrate (biochemistry)

In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or...

 using a variety of reaction mechanism

Reaction mechanism

In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs.Although only the net chemical change is directly observable for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in...

s. Cleavage

Cleavage

Cleavage may refer to:*Cleavage , partial exposure of the separation between a woman's breasts.**Cleavage enhancement, methods of making a person's breast cleavage look more substantial than it really is....

 of aromatic rings is one of the most important functions of dioxygenases, which play key roles in the degradation

Chemical decomposition

Chemical decomposition, analysis or breakdown is the separation of a chemical compound into elements or simpler compounds. It is sometimes defined as the exact opposite of a chemical synthesis. Chemical decomposition is often an undesired chemical reaction...

 of aromatic compounds. The substrates of ring-cleavage dioxygenases can be classified into two groups according to the mode of scission of the aromatic ring. Intradiol enzyme

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...

s use a non-haem Fe(III) to cleave

Bond cleavage

Bond cleavage, or scission, is the splitting of chemical bonds.If the two electrons in a cleaved covalent bond are divided between the products, the process is known as homolytic fission and free redicals are generated by homolytic cleavage the process is known as homolytic fission or homolysis...

 the aromatic ring between two hydroxyl

Hydroxyl

A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...

 groups (ortho-cleavage), whereas extradiol enzymes use a non-haem Fe(II) to cleave the aromatic ring between a hydroxylated carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 and an adjacent non-hydroxylated carbon (meta-cleavage). These two subfamilies differ in sequence, structural

Secondary structure

In biochemistry and structural biology, secondary structure is the general three-dimensional form of local segments of biopolymers such as proteins and nucleic acids...

 fold, iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 ligands, and the orientation of second sphere active site

Active site

In biology the active site is part of an enzyme where substrates bind and undergo a chemical reaction. The majority of enzymes are proteins but RNA enzymes called ribozymes also exist. The active site of an enzyme is usually found in a cleft or pocket that is lined by amino acid residues that...

 amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 residues

Residue (chemistry)

In chemistry, residue is the material remaining after a distillation or an evaporation, or to a portion of a larger molecule, such as a methyl group. It may also refer to the undesired byproducts of a reaction....

.

Enzymes that belong to the intradiol family include catechol 1,2-dioxygenase (1,2-CTD) ; protocatechuate 3,4-dioxygenase

Protocatechuate 3,4-dioxygenase

In enzymology, a protocatechuate 3,4-dioxygenase is an enzyme that catalyzes the chemical reactionThus, the two substrates of this enzyme are 3,4-dihydroxybenzoate and O2, whereas its product is 3-carboxy-cis,cis-muconate....

 (3,4-PCD) and chlorocatechol 1,2-dioxygenase 

Enzymes that belong to the extradiol class II family include catechol 2,3-dioxygenase (2,3-CTD) and biphenyl-2,3-diol 1,2-dioxygenase

Biphenyl-2,3-diol 1,2-dioxygenase

In enzymology, a biphenyl-2,3-diol 1,2-dioxygenase is an enzyme that catalyzes the chemical reactionThus, the two substrates of this enzyme are biphenyl-2,3-diol and O2, whereas its two products are 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate and H2O....

(BphC) .