Amine oxidase (copper-containing) (AOC) ( and ; formerly ) is a family of amine oxidase

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s which includes both primary-amine oxidase and diamine oxidase; these enzymes catalyze the oxidation of a wide range of

biogenic amine A biogenic amine is a biogenic substance with one or more amine groups. They are basic nitrogenous compounds formed mainly by decarboxylation of amino acids or by amination and transamination of aldehydes and ketones. Biogenic amines are o ...

s including many

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...

histamine Histamine is an organic nitrogenous compound involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Discovered in 19 ...

and xenobiotic amines. They act as a disulphide-linked

homodimer In biochemistry, a protein dimer is a macromolecular complex or protein multimer, multimer formed by two protein monomers, or single proteins, which are usually Non-covalent interaction, non-covalently bound. Many macromolecules, such as proteins ...

. They catalyse the oxidation of primary amines to aldehydes, with the subsequent release of ammonia and

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

, which requires one copper ion per subunit and topaquinone as cofactor: :RCH₂NH₂ + H₂O + O₂

\rightleftharpoons

RCHO + NH₃ + H₂O₂ The 3 substrates of this enzyme are

primary amines In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

(RCH2NH2), H₂O, and O₂, whereas its 3

products Product may refer to: Business * Product (business), an item that can be offered to a market to satisfy the desire or need of a customer. * Product (project management), a deliverable or set of deliverables that contribute to a business solution ...

are RCHO, NH₃, and H₂O₂. Copper-containing amine oxidases are found in bacteria, fungi, plants and animals. In prokaryotes, the enzyme enables various amine substrates to be used as sources of carbon and nitrogen. This enzyme belongs to

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 the CH-NH2 group of donors with oxygen as 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 semitrivi ...

of this enzyme class is amine:oxygen oxidoreductase (deaminating) (copper-containing). This enzyme participates in 8

metabolic pathways In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical ...

urea cycle and metabolism of amino groups The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions that produces urea (NH2)2CO from ammonia (NH3). Animals that use this cycle, mainly amphibians and mammals, are called ureotelic. The urea cycle converts highly ...

, glycine, serine and threonine metabolism, histidine metabolism,

tyrosine metabolism -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a conditionally essential amino acid with a polar side group. The word "tyrosine" is f ...

, phenylalanine metabolism,

tryptophan metabolism Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic ...

, beta-alanine metabolism, and alkaloid biosynthesis ii. It has 2 cofactors:

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

, and PQQ.

Structure

The copper amine oxidase 3-dimensional structure was determined through

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

. The copper amine oxidases occur as mushroom-shaped homodimers of 70-95 kDa, each monomer containing a copper ion and a covalently bound

redox cofactor A cofactor is a non-protein chemical compound or Metal ions in aqueous solution, metallic ion that is required for an enzyme's role as a catalysis, catalyst (a catalyst is a substance that increases the rate of a chemical reaction). Cofactors can ...

, topaquinone (TPQ). TPQ is formed by post-translational modification of a conserved tyrosine residue. The copper ion is coordinated with three histidine residues and two water molecules in a distorted square pyramidal geometry, and has a dual function in catalysis and TPQ biogenesis. The catalytic domain is the largest of the 3-4 domains found in copper amine oxidases, and consists of a

beta sandwich Beta-sandwich or β-sandwich domains consisting of 80 to 350 amino acids occur commonly in proteins. They are characterized by two opposing antiparallel beta sheets (β-sheets). The number of strands found in such domains may differ from one prote ...

of 18 strands in two sheets. The active site is buried and requires a conformational change to allow the substrate access. The N2 and N3 N-terminal domains share a common structural fold, its core consisting of alpha-beta(4), where the helix is packed against the coiled anti-parallel beta-sheets. An additional domain is found at the N-terminal of some copper amine oxidases, as well as in related

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s such as

cell wall A cell wall is a structural layer that surrounds some Cell type, cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, ...

hydrolase In biochemistry, hydrolases constitute a class of enzymes that commonly function as biochemical catalysts that use water to break a chemical bond: :\ce \quad \xrightarrowtext\quad \ce This typically results in dividing a larger molecule into s ...

and N-acetylmuramoyl-L-alanine

amidase In enzymology, an amidase (, ''acylamidase'', ''acylase (misleading)'', ''amidohydrolase (ambiguous)'', ''deaminase (ambiguous)'', ''fatty acylamidase'', ''N-acetylaminohydrolase (ambiguous)'') is an enzyme that catalysis, catalyzes the hydrolysis ...

. This domain consists of a five-stranded antiparallel

beta-sheet The beta sheet (β-sheet, also β-pleated sheet) is a common structural motif, motif of the regular protein secondary structure. Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone chain, backbon ...

twisted around an alpha

helix A helix (; ) is a shape like a cylindrical coil spring or the thread of a machine screw. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is for ...

Function

In eukaryotes they have a broader range of functions, including cell differentiation and growth, wound healing, detoxification and cell signalling; one AOC enzyme ( AOC3) functions as a vascular adhesion protein (VAP-1) in some mammalian tissues.

Human proteins containing this domain

* AOC1 *

AOC2 Amine oxidase, copper containing 2 (AOC2) is a protein that in humans is encoded by the ''AOC2'' gene. The protein is a copper-containing primary amine oxidase enzyme. Function Copper amine oxidases catalyze the oxidative conversion of amines ...

* AOC3

Structure

Function

Human proteins containing this domain

See also

References

Further reading