INFLUENCE OF PEROXIDASE ON THE OLIGOMERIZATION OF 5,6-DIHYDROXYTRYPTAMINE AND 5,7-DIHYDROXYTRYPTAMINE INVESTIGATED BY MATRIX-ASSISTED-LASER-DESORPTION IONIZATION MASS-SPECTROMETRY/

The influence of peroxidase in the melanogenesis of 5,6- and 5,7-dihyd roxytryptamines (DHT) was investigated by matrix-assisted laser desorp tion/ionization mass spectrometry. Incubation was carried out with per oxidase, in the presence or absence of hydrogen peroxide. Samples were withdrawn at various times, ultrafiltered to remove the enzyme and im mediately lyophilized. Reaction of the two isomers with peroxidase alo ne revealed processes similar to those observed in the case of reactio n with tyrosinase, leading to low molecular mass oligomers. Reaction w ith peroxidase and hydrogen peroxide showed very different reactivity of the two isomers. 5,6-DHT immediately led to the formation of a blac k precipitate, probably due to the reaction of its oxidation products with the enzyme. In contrast, 5,7-DHT formed oligomers, up to nonamers , originating from the molecule itself and from its oxidation products . Both isomers showed the same chemical reactivity with respect to hyd rogen peroxide alone, with the formation of up to nonamer species from both original molecules and their oxidation products. (C) 1998 John W iley & Sons, Ltd.