PMID: 9173471Mar 1, 1997Paper

New possible pathways for melanogenesis: opiomelanins

Recenti progressi in medicina
M A RoseiC De Marco

Abstract

Opioid peptides and other Tyr-NH2-terminal peptides are substrates in vitro for mushroom and sepia tyrosinase giving rise to synthetic melanins retaining the peptide moiety (opiomelanins). The melanopeptides are characterized by a total solubility in hydrophilic solvents at neutral and basic pH. Opioid peptides (enkephalins, endorphins, esorphins), if oxidized by tyrosinase in the presence of Dopa are easily incorporated into Dopa-melanin, producing mixed-type pigments which can also be solubilized in hydrophilic solvents. Melanins deriving from opioid peptides exhibit paramagnetism as evidenced by an EPR spectrum identical to that of Dopa-melanin. However the presence of the linked peptide chain is able to influence dramatically the electron transfer properties and the oxidizing behaviour of the melanopeptides, so that whereas Tyr-Gly-melanin appears to behave as Dopa-melanin, Enk-melanin does not exhibit any oxidizing activity. Opiomelanins are characterized by a peculiar UV-VIS spectrum i.e. by the presence of a well distinct peak (330 nm) disappearing upon chemical treatment by acid hydrolysis. Opiomelanins are stable pigments at neutral and basic pH in the dark, whereas H2O2 addition leads to a 15% degradation. Under simul...Continue Reading

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