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Tyrosinase




Tyrosinase (oculocutaneous albinism IA)
Identifiers
Symbol(s) TYR; OCA1A; OCAIA
External IDs OMIM: 606933 MGI: 98880 Homologene: 30969
EC number 1.14.18.1
RNA expression pattern

More reference expression data

Orthologs
Human Mouse
Entrez 7299 22173
Ensembl ENSG00000077498 ENSMUSG00000004651
Uniprot P14679 Q3UFK9
Refseq NM_000372 (mRNA)
NP_000363 (protein)
NM_011661 (mRNA)
NP_035791 (protein)
Location Chr 11: 88.55 - 88.67 Mb Chr 7: 87.3 - 87.37 Mb
Pubmed search [1] [2]

Tyrosinase (monophenol monooxygenase) (EC 1.14.18.1; CAS number: 9002-10-2) is an enzyme that catalyses the oxidation of phenols (such as tyrosine) and is widespread in plants and animals. Tyrosinase is a copper-containing enzyme present in plant and animal tissues that catalyzes the production of melanin and other pigments from tyrosine by oxidation, as in the blackening of a peeled or sliced potato exposed to air.

Additional recommended knowledge

Contents

Pathology

When a person has a mutated tyrosinase gene they have albinism, a hereditary disease that one in every 17,000 person has in the United States.

An extremely high level of tyrosinase will induce melanoma[citation needed].

Chemical reactions

Tyrosinase carries out the oxidation of phenols such as tyrosine and catechol using dioxygen (O2). In the presence of catechol, benzoquinone is formed (see reaction below). Hydrogens removed from catechol combine with oxygen to form water.

 

Tyrosinase structure

Tyrosinases have been isolated and studied from a wide variety of plant, animal and fungi species. Tyrosinases from different species are diverse in terms of their structural properties, tissue distribution and cellular location.[1] It has been suggested that there is no common tyrosinase protein structure occurring across all species.[2] The enzymes found in plant, animal and fungi tissue frequently differ with respect to their primary structure, size, glycosylation pattern and activation characteristics. However, all tyrosinases have in common a binuclear type 3 copper centre within their active site. Here two copper atoms are each coordinated with three histidine residues.

Transmembrane protein and sorting

Human tyrosinase is a single membrane spanning transmembrane protein[3]. In humans, tyrosinase is sorted into melanosomes[4] and the catalytically active domain of the protein resides within melanosomes. Only a small enzymatically non-essential part of the protein extends into the cytoplasm.

Active site

The models below are formatted from the protein data bank file 1WX3. This pdb file contains the coordinates for the crystal structure of a Streptomyces derived tyrosinase in complex with a so called "caddie protein".[5] In all models only the tyrosinase molecule is shown, copper atoms are shown in green and the molecular surface is shown in red. In models D and E histidine amino acids are shown as a blue line representation. From model E it can be clearly seen that each copper atom within the active site is indeed complexed with three histidine residues, forming a type 3 copper center. It can also be seen from models C and D that the active site for this protein sits within a pocket formed on the molecular surface of the molecule.

The two copper atoms within the active site of tyrosinase enzymes interact with dioxygen to form a highly reactive chemical intermediate that then oxidizes the substrate. The activity of tyrosinase is similar to catechol oxidase, a related class of copper oxidase. Tyrosinases and catechol oxidases are collectively termed polyphenol oxidases

 

References

  1. ^ Mayer, AM (2006). "Polyphenol oxidases in plants and fungi: Going places? A review". Phytochemistry 67: 2318-2331. PMID 16973188.
  2. ^ Jaenicke, E and Decker, H. (2003). "Tyrosinases from crustaceans form hexamers". Biochem. J. 371: 515-523. PMID 12466021.
  3. ^ Isolation and sequence of a cDNA clone for human tyrosinase that maps at the mouse c-albino locus by B. S. Kwon, A. K. Haq, S. H. Pomerantz and R. Halaban in Proceedings of the National Academy of Sciences (1987) Volume 84, pages 7473–7477.
  4. ^ Functions of Adaptor Protein (AP)-3 and AP-1 in Tyrosinase Sorting from Endosomes to Melanosomes by Alexander C. Theos, Danièle Tenza, José A. Martina, Ilse Hurbain, Andrew A. Peden, Elena V. Sviderskaya, Abigail Stewart, Margaret S. Robinson, Dorothy C. Bennett, Daniel F. Cutler, Juan S. Bonifacino, Michael S. Marks and Graça Raposo in Molecular Biology of the Cell (2005) Volume 16, pages 5356–5372.
  5. ^ Matoba Y, Kumagi, T. et al (2006). "Crystallographic evidence that the dinuclear copper center of tyrosinase is flexible during catalysis". J. Biol. Chem. 281 (13): 8981-8990. PMID 16436386.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Tyrosinase". A list of authors is available in Wikipedia.
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