Oxidation of the indole nucleus of 5-hydroxytryptamine and formation of dimers in the presence of peroxidase and H2O2

5-Hydroxytryptamine (5-HT) is rapidly oxidized in the presence of peroxidase and H2O2. The major reaction product was isolated by gel chromatography and analyzed by mass spectroscopy. It is a 5-HT dimer formed under abstraction of two protons, most likely by the reaction at the C(4) position of two phenoxyradicals of 5-HT. In the presence of 5-HT an increased H2O2-consumption and a dose dependent reduction of the formation of reactive oxygen metabolites during H2O2 degradation was observed. The pattern of 5-HT reaction products separated by TLC was dependent on the H2O2 concentrations used. In the presence of albumen, plasma or tissue homogenates, massive binding of the 5-HT oxidation products to proteins was observed.