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Some biochemical properties of melanins from opioid peptides

1994; Elsevier BV; Volume: 1199; Issue: 2 Linguagem: Inglês

10.1016/0304-4165(94)90106-6

1872-8006

Maria Anna Rosei, Luciana Mosca, Raffaella Coccia, Carla Blarzino, Giovanni Musci, Carlo De Marco,

Protein Hydrolysis and Bioactive Peptides

Opioid peptides are converted by mushroom tyrosinase into melanin-like compounds retaining the peptide moiety (opio-melanins). Opio-melanins, owing to the presence of the linked aminoacids and in contrast with DOPA-melanin, are soluble compounds. The enkephalin-generated melanins are cleaved by carboxypeptidase A and pronase whereas aminopeptidase M cannot remove aminoacids from the pigment. Enkephalins, as well as other opioid peptides, (alpha-endorphin, kyotorphin, esorphins) if oxidized in presence of DOPA and tyrosinase are readily incorporated into DOPA-melanin. The resulting mixed-melanins (opio-melanin + DOPA-melanin) can be solubilized in hydrophilic solvents. Melanin from leu-enkephalin exhibits paramagnetism as evidenced by an EPR spectrum identical to that of DOPA-melanin, but unlike the latter pigment, it does not appear to oxidize NADH, probably for the presence of the peptide moiety that exerts a hampering effect on the oxidizing capacity.