Some biochemical properties of melanins from opioid 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.
Rosei
M A
MA
Department of Biochemical Sciences, Piazza A. Moro, 5, Rome, Italy.
Mosca
L
L
Coccia
R
R
Blarzino
C
C
Musci
G
G
De Marco
C
C
D000595:Amino Acid Sequence; D000626:Aminopeptidases / Q000378:metabolism; D001487:Basidiomycota / Q000201:enzymology; D018826:CD13 Antigens; D002268:Carboxypeptidases / Q000378:metabolism; D043422:Carboxypeptidases A; D004295:Dihydroxyphenylalanine / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004723:Endorphins / Q000737:chemistry* / Q000378:metabolism; D004745:Enkephalins / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008543:Melanins / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D014442:Monophenol Monooxygenase / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D011402:Pronase / Q000378:metabolism; D012995:Solubility
D004723:Endorphins; D004745:Enkephalins; D008543:Melanins; D009243:NAD; D004295:Dihydroxyphenylalanine; D014442:Monophenol Monooxygenase; D002268:Carboxypeptidases; D000626:Aminopeptidases; D018826:CD13 Antigens; D043422:Carboxypeptidases A; D011402:Pronase