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An investigation on the role of 3‐hydroxykynurenine in pigment formation by matrix‐assisted laser desorption/ionization mass spectrometry
Author(s) -
Vogliardi Susanna,
Bertazzo Antonella,
Comai Stefano,
Costa Carlo V. L.,
Allegri Graziella,
Seraglia Roberta,
Traldi Pietro
Publication year - 2004
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.1497
Subject(s) - chemistry , mass spectrometry , desorption , tyrosinase , peroxidase , pigment , matrix (chemical analysis) , ionization , photochemistry , enzyme , chromatography , organic chemistry , adsorption , ion
In order to investigate the role of tryptophan and its metabolites in biogenesis of melanins, a study on the enzymatic reaction of 3‐hydroxykynurenine with tyrosinase and peroxidase was performed. The reaction at different pH values was monitored by sampling at different times, with ultrafiltration used before analysis by matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS). The data obtained in this way showed that oligomerization processes take place with both enzymes, but with different behaviour, also depending on pH. 3‐Hydroxykynurenine in the presence of tyrosinase at pH 6.0 leads to formation of xanthommatin, and at pH 8.0 hydroxanthommatin is formed in the first step of the reaction followed by formation of black‐brown pigments. In contrast, the formation of oligomerization products by peroxidase action is observed in high yields under both acidic and basic conditions; however, at pH 6.0, a more extensive oligomerization process is observed. Thus peroxidase is able to activate oligomerization analogous to that observed in the case of tyrosinase without depending on the variation of pH. Due to the early formation of decarboxylated hydroxykynurenine, hydroxanthommatin and decarboxylated hydroxanthommatin, the enzymatic reaction leads to mixed oligomers, which can be considered as precursors of new pathways in pigment production. Copyright © 2004 John Wiley & Sons, Ltd.