An investigation on the role of 3-hydroxykynurenine in pigment formation by matrix-assisted laser desorption/ionization mass spectrometry

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

An investigation of the aroma fraction of some Italian wines by solid phase micro extraction gas chromatography mass spectrometry and membrane inlet mass spectrometry

Two analytical approaches have been applied to the characterization of the aroma fraction of five Italian wines, solid-phase micro-extraction coupled with gas chromatography, and membrane inlet mass spectrometry. The first approach resulted in highly specific and reproducible data and permitted the differentiation among wine samples from the same grape but from different production areas. The second technique, notable for its short time of analysis and ease of use, exhibited a lower specificit

Quinoa: protein and nonprotein tryptophan in comparison with other cereal and legume flours and bread

\u2022 nutritional value of bread can be improved making composite flours with non wheat cereals or supplementing its flour with protein-rich sources, such as legume flours, especially in the several countries where the production of wheat is insufficient; \u2022 quinoa can be an alternative to cereals in the human diet for its nutritional value and high good quality proteins similar to those of milk, and for these reasons, its use should be promoted to enrich the nutritional value of bakery products; \u2022 tryptophan is present in cereals and legumes not only as protein tryptophan but also as non protein tryptophan (Figure 7); \u2022 non protein tryptophan should be taken into account when the nutritional value of a food is determined; \u2022 the determination of non protein tryptophan in cereals and legumes is very important since this fraction is easily absorbable at the gastrointestinal level increasing its availability for brain serotonin synthesis

Enzyme activities along the kynurenine pathway in mice

Tryptophan metabolism was studied in adult male Swiss mice by determining enzyme activities along the kynurenine pathway. The following enzymes were assayed: liver tryptophan 2,3-dioxygenase, small intestine indole 2,3-dioxygenase, liver and kidney kynurenine 3-monooxygenase, kynureninase, kynurenine-oxoglutarate transaminase, 3-hydroxyanthranilate 3,4-dioxygenase, and aminocarboxymuconate-semialdehyde decarboxylase. Liver tryptophan 2,3-dioxygenase was present only as a holoenzyme: similar results were obtained in the absence or in the presence of the cofactor haematin. The specific activity of small intestine indole 2,3-dioxygenase was higher than that of tryptophan 2,3-dioxygenase. As superoxide dismutase was very active in mouse intestine, this enzyme may be one of the rate controlling factors of the indole 2,3 dioxygenase activity. Kynurenine 3-monooxygenase appeared to be very active. Kidneys showed higher activity than liver. Instead, kynureninase was more active in liver, but activity was lower than that demonstrated by the other enzymes of the kynurenine pathway. Conversely, kynurenine-oxoglutarate transaminase was much more active in kidney than in liver. However, the most active enzyme along the kynurenine pathway was 3-hydroxyanthranilate 3,4-dioxygenase, with liver showing the highest activity; aminocarboxymuconate-semialdehyde decarboxylase, which showed similar values in both liver and kidney, showed activity markedly lower than 3-hydroxyanthranilate 3,4-dioxygenase. Serum tryptophan appeared to be 87% bound to proteins. Results demonstrate that, in mouse, tryptophan is mainly metabolised along the kynurenine pathway. Therefore, mouse is a suitable animal model for studying tryptophan metabolism in the pathological field