P-209 - Scavenging activity of free and peptide tryptophan and tyrosine residues towards AAPH-derived free radicals

Abstract

The scavenging activity of free and peptide-included tryptophan (Trp) and tyrosine (Tyr) residues towards AAPH (2,2’-azobis(2-amidinopropane) dihydrochloride)-derived free radicals, was evaluated through the ORAC (Oxygen Radical Absorbance Capacity) assay. Employing fluorescein (ORAC-Fl) as probe the ORAC index renders values towards alkoxyl radicals (RO•), while the use of pyrogallol red (ORAC-PGR), and pyranine (ORAC-Pyr) reflects values towards peroxyl radicals (ROO•). Free Trp showed an ORAC-Fl value (ORAC-Fl=5.0) between 1.4 and 2.2 times lower than Trp-Ala, Trp-Phe, Trp-Gly, Gly-Trp, and Gly-Trp-Gly. These tendencies, which was in agreement with kinetic parameters, showed an antioxidant capacity towards RO• in the same order of magnitude that Trolox. Towards ROO, ORAC-like assays showed very low scavenging activities for free and peptide Trp (without protection of PGR) with values hundred times lower than Trolox. Free and peptide Tyr residues showed significantly lower ORAC-Fl and ORAC-Py values than Trp. These data evidenced the influence of the inclusion of Trp and Tyr in peptides on the scavenging activity, as well as, the relevance of reactions involving RO• in the ORAC assay.