Kinetics of the chemiluminescence associated to the reaction between peroxyl radicals and proteins

Protein oxidation, mediated by peroxyl radicals derived from 2,2'-azobis(2- amidinopropane) dihydrochloride is sided by a significant visible chemilumi nescence (CL). The Light emission shows a complex dependence with the prote in concentration and with the incubation time that cannot be interpreted in terms of peroxyl radicals recombination (Russell's mechanism). In all the systems studied, the chemiluminescent behavior requires to consider the par ticipation of several oxidation products as precursors of the excited state s. These compounds lead to the formation of excited states by competing rad ical and nonradical mediated pathways. These intermediates (most probably h ydroperoxide-like compounds) would arise from the oxidation of Trp and Tyr residues. This conclusion is based on the similarity of the time profile of the chemiluminescence observed in the oxidation of the free amino acids an d the proteins, both in the presence of and absence of free-radical scaveng ers.