Amicyanin is a type I copper protein

Copper proteins

Copper proteins are proteins that contain one or more copper ions as prosthetic groups. The metal centres in the copper proteins can be classified into several types:...

 that plays an integral role in electron transfer. In bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 such as Paracoccus denitrificans

Paracoccus denitrificans

Paracoccus denitrificans, is a coccoid bacterium known for its nitrate reducing properties, its ability to replicate under conditions of hypergravity and for being the possible ancestor of the eukaryotic mitochondrion .-Description:...

, amicyanin is part of a three-member redox

Redox

Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 complex

Complex

A complex is a whole that comprehends a number of intricate parts, especially one with interconnected or mutually related parts; for example, a complex of buildings.Complex may refer to:-Biology:...

, along with methylamine dehydrogenase (MADH) and cytochrome

Cytochrome

Cytochromes are, in general, membrane-bound hemoproteins that contain heme groups and carry out electron transport.They are found either as monomeric proteins or as subunits of bigger enzymatic complexes that catalyze redox reactions....

 c-551i.

Function

In the electron transfer mechanism from MADH to heme

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...

, amicyanin acts as an electron accepting intermediate. In this reaction, MADH catalyzes the oxidative deamination of methylamine

Methylamine

Methylamine is the organic compound with a formula of CH3NH2. This colourless gas is a derivative of ammonia, but with one H atom replaced by a methyl group. It is the simplest primary amine. It is sold as a solution in methanol, ethanol, THF, and water, or as the anhydrous gas in pressurized...

 to formaldehyde

Formaldehyde

Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...

 plus ammonia

Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

. The tryptophan tryptophylquinone

Tryptophan tryptophylquinone

Tryptophan tryptophylquinone is a molecule required for the functioning of amine dehydrogenase....

 (TTQ) group of MADH then donates electrons to the copper center of amicyanin, which in turn gives the electrons to the heme of the cytochrome c. In P. denitrificans, amicyanin is absolutely required for electron transfer from MADH to c-type cytochromes. It has been shown that inactivation of amicyanin by gene replacement in vivo results in complete loss of ability to grow on methylamine.

Structure

As a type I copper protein, amicyanin contains one copper atom coordinated by two histidine

Histidine

Histidine Histidine, an essential amino acid, has a positively charged imidazole functional group. It is one of the 22 proteinogenic amino acids. Its codons are CAU and CAC. Histidine was first isolated by German physician Albrecht Kossel in 1896. Histidine is an essential amino acid in humans...

 residues and a cysteine

Cysteine

Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...

 residue in a trigonal planar structure along with an axial methionine

Methionine

Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein...

 residue ligand

Ligand

In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...

. Alterations from this particular coordination of the copper center are found to negatively alter the redox potential of amicyanin.
In P. denitrificans, amicyanin exists in a three-part complex along with MADH and cytochrome c-551i. This is the only redox complex composed of three weakly associated proteins naturally observed.