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.

Cryptic Color Change in a Crab Spider (Misumena vatia): Identification and Quantification of Precursors and Ommochrome Pigments by HPLC

“…It is unclear if Dc-xanthommatin is an artifact of processing the samples or a true metabolite present in living spiders. Vogliardi et al (2004) suggest that this compound could be a precursor of new pathways to ommochrome production. In this study, the principal component analysis revealed that the amounts of Dc-xanthommatin are independent of the amounts of other metabolites that give the yellow colora- Mean values correspond to the results of four independent assays for each color of crab spider (means ± S.D.).…”

Ommochromes in invertebrates: biochemistry and cell biology

“…B) (Linzen, ; Needham, ; Kayser, ). The most recently identified ommochromes are the decarboxylated forms of xanthommatin and H 2 ‐xanthommatin, which were first found in in vitro oxidation of ommochrome precursors (Bolognese et al, ; Vogliardi et al, ) but were subsequently described in extracts of crab spiders, dragonflies, silkworms and cephalopods (Riou & Christidès, ; Futahashi et al, ; Osanai‐Futahashi et al, ; Williams et al, ). Unfortunately, almost nothing is known about ommidins.…”

“…Today, with more sensitive detectors available, the absorption spectra of compounds even at very low concentrations can be measured using high‐pressure liquid chromatography (HPLC) (Riou & Christidès, ; Llandres et al, ). The increasing availability of mass spectrometry (MS) further enhances the identification power for both known and unknown ommochromes (Table ) (Vogliardi et al, ; Daniels & Reed, ; Futahashi et al, ; Williams et al, ). The ommochrome field would benefit from the creation of a community‐based MS library (Dunn et al, ) containing precursor and fragment ions from a large range of ommochromes and phenoxazone‐based compounds (Table ).…”

Two complex genotypes relevant to the kynurenine pathway and melanotropin function show association with schizophrenia and bipolar disorder

“…This interpretation of the pathophysiology relates to the gene-gene interaction of HM74A and MCHR1 (Model 2 in Figure 1, wherein the pigment products may not be adequately sequestered when the risk genotype for MCHR1 is present combined with the risk genotype for HM74A, as the ligand for HM74A (niacin) controls levels of kynurenine pathway products in human subjects (Hankes et al, 1971). The types of kynurenine pathway pigments range from the xanthomattins, a form that predominates in the eye and thought to be involved in cataract formation (Vazquez et al, 2000) to the melanin family of pigments (Vogliardi et al,2004), to the antibiotic, cinnabarinic acid (Vazquez et al, 2000). As a general class, the toxicity of pigment molecules and their reactive precursors has been well recognized, including the well-known kernicterus induced by bilirubin pigment and the toxicity of neuromelanin when it is not adequately sequestered (Offen et al, 1997).…”