Portal de Periódicos da CAPES

Application of matrix-assisted laser desorption/ionization mass spectrometry to the detection of melanins formed from Dopa and dopamine

1999; Wiley; Volume: 34; Issue: 9 Linguagem: Inglês

10.1002/(sici)1096-9888(199909)34

1096-9888

Antonella Bertazzo, Carlo Costa, Graziella Allegri, Donata Favretto, Pietro Traldi,

melanin and skin pigmentation

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry was used to study melanogenesis starting from Dopa and dopamine, the latter considered one of the precursors of neuromelanins. These substrates were left to react with the peroxidase – H2O2 system, which is postulated to play an important role in melanin biosynthesis. Samples were prepared by ultrafiltering the substrate – enzyme solution after 30, 60, 120, 240 and 360 min of reaction and aliquots were immediately lyophilized. The reaction of dopamine with peroxidase – H2O2 favoured the formation of dopamine oligomers up to octamers. In contrast, the action of either peroxidase or H2O2 alone, studied for comparison, did not lead to melanin production and only dimeric and trimeric species were observed. Also for Dopa, analogous results were obtained in the presence of either peroxidase or H2O2 alone, without melanin formation. Conversely, Dopa with the peroxidase – H2O2 system led to the formation of a black precipitate after 120 min of reaction, and oligomers of 5,6-dihydroxyindole (DHI), an intermediate of melanogenesis, were detected, together with products of further oxidation. Faster kinetics were observed when Dopa was treated with tyrosinase, the enzyme catalysing the oligomerization of tyrosine to melanins, leading to the formation mainly of DHI oligomers. Copyright © 1999 John Wiley & Sons, Ltd.