title: An investigation on the role of 3-hydroxykynurenine in pigment formation by matrix-assisted laser desorption/ionization mass spectrometry.
abstract: 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.
authors.affiliation: CNR, Istituto di Scienze e Tecnologie Molecolari, Corso Stati Uniti 4, I-35100 Padova, Italy.
authors.forename: Susanna
authors.initials: S
authors.lastname: Vogliardi
authors.forename: Antonella
authors.initials: A
authors.lastname: Bertazzo
authors.forename: Stefano
authors.initials: S
authors.lastname: Comai
authors.forename: Carlo V L
authors.initials: CV
authors.lastname: Costa
authors.forename: Graziella
authors.initials: G
authors.lastname: Allegri
authors.forename: Roberta
authors.initials: R
authors.lastname: Seraglia
authors.forename: Pietro
authors.initials: P
authors.lastname: Traldi
mesh_terms: D000363:Agaricales / Q000378:metabolism*; D007737:Kynurenine / Q000031:analogs & derivatives* / Q000378:metabolism*; D015394:Molecular Structure; D014442:Monophenol Monooxygenase / Q000737:chemistry; D010860:Pigments, Biological / Q000096:biosynthesis*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013329:Structure-Activity Relationship; D014364:Tryptophan / Q000096:biosynthesis
chemical_list: D010860:Pigments, Biological; C005045:3-hydroxykynurenine; D007737:Kynurenine; D014364:Tryptophan; D014442:Monophenol Monooxygenase