Reaction: (1) L-tyrosine + O2 = dopaquinone + H2O (overall reaction)
(1a) L-tyrosine + ½ O2 = L-dopa
(1b) L-dopa + ½ O2 = dopaquinone + H2O
(2) 2 L-dopa + O2 = 2 dopaquinone + 2 H2O
For diagram of reaction click here.
Other name(s): monophenol monooxygenase; phenolase; monophenol oxidase; cresolase; monophenolase; tyrosine-dopa oxidase; monophenol monooxidase; monophenol dihydroxyphenylalanine:oxygen oxidoreductase; N-acetyl-6-hydroxytryptophan oxidase; monophenol, dihydroxy-L-phenylalanine oxygen oxidoreductase; o-diphenol:O2 oxidoreductase; phenol oxidase
Systematic name: L-tyrosine,L-dopa:oxygen oxidoreductase
Comments: A type III copper protein found in a broad variety of bacteria, fungi, plants, insects, crustaceans, and mammals, which is involved in the synthesis of betalains and melanin. The enzyme, which is activated upon binding molecular oxygen, can catalyse both a monophenolase reaction cycle (reaction 1) or a diphenolase reaction cycle (reaction 2). During the monophenolase cycle, one of the bound oxygen atoms is transferred to a monophenol (such as L-tyrosine), generating an o-diphoenol intermediate, which is subsequently oxidized to an o-quinone and released, along with a water molecule. The enzyme remains in an inactive deoxy state, and is restored to the active oxy state by the binding of a new oxygen molecule. During the diphenolase cycle the enzyme binds an external diphenol molecule (such as L-dopa) and oxidizes it to an o-quinone that is released along with a water molecule, leaving the enzyme in the intermediate met state. The enzyme then binds a second diphenol molecule and repeats the process, ending in a deoxy state . The second reaction is identical to that catalysed by the related enzyme catechol oxidase (EC 18.104.22.168). However, the latter can not catalyse the hydroxylation or monooxygenation of monophenols.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number: 9002-10-2
1. Dawson, C.R. and Tarpley, W.B. The copper oxidases. In: Sumner, J.B. and Myrbäck, K. (Eds), The Enzymes, 1st edn, vol. 2, Academic Press, New York, 1951, pp. 454-498.
2. Patil, S.S. and Zucker, M. Potato phenolases. Purification and properties. J. Biol. Chem. 240 (1965) 3938-3943. [PMID: 5842066]
3. Pomerantz, S.H. Separation, purification, and properties of two tyrosinases from hamster melanoma. J. Biol. Chem. 238 (1963) 2351-2357. [PMID: 13972077]
4. Robb, D.A. `Tyrosinase. In: Lontie, R. (Ed.), Copper Proteins and Copper Enzymes, vol. 2, CRC Press, Boca Raton, FL, 1984, pp. 207-240.
5. Sanchez-Ferrer, A., Rodriguez-Lopez, J.N., Garcia-Canovas, F. and Garcia-Carmona, F. Tyrosinase: a comprehensive review of its mechanism. Biochim. Biophys. Acta 1247 (1995) 1-11. [PMID: 7873577]
6. Steiner, U., Schliemann, W. and Strack, D. Assay for tyrosine hydroxylation activity of tyrosinase from betalain-forming plants and cell cultures. Anal. Biochem. 238 (1996) 72-75. [PMID: 8660589]
7. Rolff, M., Schottenheim, J., Decker, H. and Tuczek, F. Copper-O2 reactivity of tyrosinase models towards external monophenolic substrates: molecular mechanism and comparison with the enzyme. Chem Soc Rev 40 (2011) 4077-4098. [PMID: 21416076]