Recently our group synthesized a new class of melanins obtained by the tyrosinase-catalyzed oxidation of opioid peptides (opiomelanins). Owing to the presence of the peptide moiety such pigments exhibit high solubility in hydrophilic solvents, which allows spectroscopic investigations. In particular, the absence of solid-state quenching effects enables the study of melanin fluorescence properties, till now poorly investigated due to the complete insolubility of melanins produced from tyrosine or Dopa. Opiomelanins dissolved in acqueous medium show a characteristic emission peaked at 440 and 520 nm when excited around 330 nm, where a maximum is observed in the absorption spectrum. Kinetic measurements performed on the tyrosinase-catalyzed oxidation of opioid peptides show that the 440-nm fluorescence band arises in the early stages of peptide oxidation, whereas the 520-nm band appears in later stages of oxidation, i.e., during the polymerization of indole-quinone units. Moreover, molecular sieve fractionation shows that in the opiomelanin fraction with a molecular weight lower than 10 kDa the 440-nm band is dominant in the fluorescence spectrum. The breakdown of the polymer induced by hydrogen peroxide and light (i.e., the photobleaching of melanin pigments) produces a marked enhancement of the 440-nm fluorescence band while the 520-nm band disappears. Hence, our findings suggest that the observed fluorescence contains contributions from both oligomeric units (440-nm band) and high-molecular-weight polymers (520-nm band). (C) 1999 Academic Press.

Fluorescence properties of melanins from opioid peptides / Mosca, Luciana; DE MARCO, Carlo; Fontana, Mario; Rosei, Maria Anna. - In: ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS. - ISSN 0003-9861. - STAMPA. - 371:1(1999), pp. 63-69. [10.1006/abbi.1999.1403]

Fluorescence properties of melanins from opioid peptides

MOSCA, Luciana;DE MARCO, Carlo;FONTANA, Mario;ROSEI, Maria Anna
1999

Abstract

Recently our group synthesized a new class of melanins obtained by the tyrosinase-catalyzed oxidation of opioid peptides (opiomelanins). Owing to the presence of the peptide moiety such pigments exhibit high solubility in hydrophilic solvents, which allows spectroscopic investigations. In particular, the absence of solid-state quenching effects enables the study of melanin fluorescence properties, till now poorly investigated due to the complete insolubility of melanins produced from tyrosine or Dopa. Opiomelanins dissolved in acqueous medium show a characteristic emission peaked at 440 and 520 nm when excited around 330 nm, where a maximum is observed in the absorption spectrum. Kinetic measurements performed on the tyrosinase-catalyzed oxidation of opioid peptides show that the 440-nm fluorescence band arises in the early stages of peptide oxidation, whereas the 520-nm band appears in later stages of oxidation, i.e., during the polymerization of indole-quinone units. Moreover, molecular sieve fractionation shows that in the opiomelanin fraction with a molecular weight lower than 10 kDa the 440-nm band is dominant in the fluorescence spectrum. The breakdown of the polymer induced by hydrogen peroxide and light (i.e., the photobleaching of melanin pigments) produces a marked enhancement of the 440-nm fluorescence band while the 520-nm band disappears. Hence, our findings suggest that the observed fluorescence contains contributions from both oligomeric units (440-nm band) and high-molecular-weight polymers (520-nm band). (C) 1999 Academic Press.
1999
enkephalins; fluorescence spectroscopy; melanin; opiomelanin
01 Pubblicazione su rivista::01a Articolo in rivista
Fluorescence properties of melanins from opioid peptides / Mosca, Luciana; DE MARCO, Carlo; Fontana, Mario; Rosei, Maria Anna. - In: ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS. - ISSN 0003-9861. - STAMPA. - 371:1(1999), pp. 63-69. [10.1006/abbi.1999.1403]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/244207
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