engleski

The role of methylglyoxal in the non-enzymatic conversion of tryptophan, its methyl ester and tryptamine to 1-acetyl-beta-carbolines

Non-enzymatic modi. cation of L-tryptophan ( 1) and its metabolites and derivatives with aldehydes, via the Pictet-Spengler reaction, affords beta-carbolines. Here we demonstrate that methylglyoxal ( 2) generates 1-acetyl-beta-carbolines from tryptophan ( 1), from its methyl ester ( 6) and from tryptamine ( 4) ; however, 2 did not generate 1-(1-hydroxyethyl)-beta-carboline derivates. HPLC analysis of model reaction systems showed formation of 1-acetyl-beta-carboline ( 3) and 1-acetyl-beta-carboline-3-carboxylic acid ( 5) during incubation of 1 and 2, at pH 5.7 and 7.4, at 100 degrees C, and only 5 at 37 degrees C, at the same pH values, with limited access of oxygen. Aerobic conditions caused higher formation of 3 at 37 degrees C at both pH values, while, at higher temperature, the same effect was only observed at pH5.7. Lack of oxygen did not much influence the formation of 3 or 5 at both pH and temperature values, in comparison with the formation at limited access of oxygen. Incubation of 2 and 6 generated methyl-1-acetyl-beta-carboline-3-carboxylate ( 7) together with 3 and 5 as a result of hydrolysis of 6 into 1 and, partially, 7 into 5, while in incubation mixtures of 2 and 4 only unstable 1-acetyl-3, 4-dihydro-beta-carboline ( 8) was observed. Incubation of 1 with D-glucose as well as incubation of tryptophan with Amadori product 18 under similar conditions did not generate carbolines 3 or 5. For the first time, we were able to demonstrate the presence of 1-acetyl-beta-carboline-3-carboxylic acid ( 5) in some commercially available ketchups and in previously heated tomato concentrate. (c) 2008 Elsevier Ltd. All rights reserved.

methylglyoxal ; Maillard ; beta-carbolines ; tryptophan

nije evidentirano