DHI and DHICA polymerise forming eumelanin

Stable Identifier
Reaction [BlackBoxEvent]
Homo sapiens
Locations in the PathwayBrowser

Eumelanin is a stacked, aggregated oligomer, or heterogeneous polymer consisting of units representing different oxidative states of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA), plus pyrrole units derived from their peroxidative cleavage (Meredith & Sarna 2006, Ito & Wakamatsu 2008). Eumelanin was thought to consist mostly of DHI but this was reconsidered when chemical degradation revealed that natural eumelanins include DHI and DHICA units in a nearly equal ratio (Ito 1986, d'Ischia et al. 2013). DHICA is produced by tautomerization of dopachrome.The oxidative polymerization of DHI can be catalyzed by Tyrosinase (TYR) (Tripathi et al. 1992) but may also be effectively catalysed by redox exchange with dopaquinone (Edge et al. 2006). Redox is likely to be less efficient for DHICA. In mice, the tyrosinase-related protein Tyrp1 can oxidize DHICA (Kobayashi et al. 1994) but human TYRP1 is unable to catalyze the same reaction (Boissy et al. 1998). Instead, human TYR oxidizes DHICA, DHI, tyrosine and dopa.

Literature References
PubMed ID Title Journal Year
17083485 The physical and chemical properties of eumelanin Pigment Cell Res. 2006
Participant Of
Catalyst Activity
Catalyst Activity
monooxygenase activity of TYR:2xCu2+ [melanosome membrane]
Physical Entity
Orthologous Events