Melanins: Skin Pigments and Much More—Types, Structural Models, Biological Functions, and Formation Routes

Figure 10

GHB-melanin formation: this melanin is only formed in mushroom and some other basidiomycetes. The first precursor is p-aminophenol which is conjugated with glutamate to form glutaminyl-hydroxy-benzene (GHB), the characteristic precursor for this route. This monophenol is oxidized by mushroom tyrosinase in a two-step reaction (see Raper-Mason pathway) to yield glutaminylbenzoquinone (GBQ). The glutamyl moiety is released to 2-hydroxy-p-iminobenzoquinone (HpIBQ), the real polymerizing species, although small amounts of previous intermediates carrying the glutamyl side chain can be incorporated to the final pigment during the last phase of the polymerization.