Biosynthetic Pathways
The first step of the biosynthetic pathway for both eumelanins and pheomelanins is catalysed by tyrosinase:
- Tyrosine → DOPA → dopaquinone
Dopaquinone can combine with cysteine by two pathways to benzothiazines and pheomelanins
- Dopaquinone + cysteine → 5-S-cysteinyldopa → benzothiazine intermediate → pheomelanin
- Dopaquinone + cysteine → 2-S-cysteinyldopa → benzothiazine intermediate → pheomelanin
Alternatively, dopaquinone can be converted to leucodopachrome and follow two more pathways to the eumelanins
- Dopaquinone → leucodopachrome → dopachrome → 5,6-dihydroxyindole-2-carboxylic acid → quinone → eumelanin
- Dopaquinone → leucodopachrome → dopachrome → 5,6-dihydroxyindole → quinone → eumelanin
Detailed metabolic pathways can be found in the KEGG database (see External links).
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