A pulse radiolysis investigation of the oxidation of the melanin precursors 3,4-dihydroxyphenylalanine (dopa) and the cysteinyldopas

Tyrosinase and related proteins in mammalian pigmentation

“…The kinetics of reaction between sulfhydryl compound and DOPAquinone is much more rapid than the cyclization of DOPAquinone into LeucoDOPAchrome [40], and, thus, the concentrations of cysteine are critical for the type of melanin synthetized.…”

Pulsed irradiation studies of some reactive intermediates of melanogenesis

“…One-electron oxidation of dihydroxyphenylalanine, dopa, v/a pulse radiolysis of an aqueous solution containing excess azide and nitrous oxide [7,8] led to the oscilloscope traces illustrated in Figure 3. Trace (a) of this Figure shows the rapid one-electron oxidation of dopa to form the semiquinone which decays over hundreds of #s into a species with absorption maximum around 380-400 nm, attributed to dopaquinone.…”

The physical and chemical properties of eumelanin

“…It is important to keep in mind that even though the redox properties of melanin are reasonably well described by the chemical properties of the melanin units significant differences exist between the melanin units and their free monomeric forms. The most obvious difference is chemical reactivity; while free ortho-quinones and orthosemiquinones are very unstable and react with other molecules (Monks et al, 1992;Thompson et al, 1985), the related melanin subunits are quite stable and exhibit substantially lower reactivity. It can be speculated that the reduced reactivity of melanin subunits is due to their restricted accessibility as a result of intramolecular interactions and steric hindrance.…”