Investigation on Melanin Biosynthesis from 5,6-Dihydroxytryptamine by Matrix-assisted Laser Desorption/Ionization Mass Spectrometry

✍ Scribed by Graziella Allegri; Antonella Bertazzo; Carlo Costa; Roberta Seraglia; Pietro Traldi

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 470 KB
• Volume: 10
• Category: Article
• ISSN: 0951-4198
• DOI: 10.1002/(sici)1097-0231(19960315)10:4<419::aid-rcm486>3.0.co;2-3

✦ Synopsis

The biosynthesis of melanin from 5,6-dihydroxytryptamine (5,6-DHT) was investigated by matrix-assisted laser desorption/ionization mass spectrometry. Melanins were obtained from the reaction between mushroom tyrosinase and 5,6-DHT under an oxygen stream. Reaction intermediates were studied by drawing samples at various reaction times by ultrafiltration to remove the enzyme, and immediately lyopbilizing. In the early stages of the oligomerization reaction (30 min reaction time), a series of ionic species at m/z 383, 573, 763, 953, 1143, 1333 and 1523 became detectable and corresponded to oligomerization products of 5,6-DHT, starting from the dimer (m/z383) and going up to the octamer (mIz1523). Increasing the reaction time to 120 min gave oligomerization products at m/z 1523 and 1710 (corresponding to octamer and nonamer respectively), with a decrease in the abundance of low molecular weight oligomers. Passing to 240 mia, the most abundant species were detectable at m/z 932, showing that other processes take place besides simple oligomerization. The oligomeric species at m/z 932 becomes the initiator of further polymerization, forming species at m/z 1857 and 2774, which may be considered the dimer and trimer of the species at m/z 932 after oxidation. The presence of the ion at m/z 932 in the samples left to react after ultrafiltration under an oxygen stream for 24 h proved that it originated from oxidation processes subsequent to oligomerization. The species at m/z 932, different in mass from the pentamer by 21 mass units, may originate from intramolecular cyclization, leading to a thermodynamically stable macrocyclic Structure.