TY - JOUR

T1 - Oxidation of free, peptide and protein tryptophan residues mediated by AAPH-derived free radicals: role of alkoxyl and peroxyl radicals

AU - Fuentes-Lemus, E.

AU - Dorta, E.

AU - Escobar, E.

AU - Aspee, A.

AU - Pino, E.

AU - Abasq, M.L.

AU - Speisky, H.

AU - Silva, E.

AU - Lissi, E.

AU - Davies, Michael Jonathan

AU - Lopez-Alarcon, C.

PY - 2016

Y1 - 2016

N2 - The oxidation of tryptophan (Trp) residues, mediated by peroxyl radicals (ROOc), follows a complexmechanism involving free radical intermediates, and short chain reactions. The reactivity of Trp towardsROOc should be strongly affected by its inclusion in peptides and proteins. To examine the latter, weinvestigated (by fluorescence) the kinetic of the consumption of free, peptide- and protein-Trp residuestowards AAPH (2,20-azobis(2-amidinopropane)dihydrochloride)-derived free radicals. Interestingly, theinitial consumption rates (Ri) were only slightly influenced by the inclusion of Trp in small peptides andproteins (human serum albumin and human superoxide dismutase). Depending on the Trpconcentration, the Ri versus Trp concentration ([Trp]) plots showed three regions. At low Trpconcentrations (1–10 mM), a linear dependence was observed between Ri and [Trp]; at intermediate Trpconcentrations (10–50 mM), the values of Ri were nearly constant; and at high Trp concentrations (50 mMto 1 mM), a slower increase of Ri than expected for chain reactions. Similar behavior was detected for allthree systems (free Trp, and Trp in peptides and proteins). For the first time we are showing that alkoxylradicals, formed from self-reaction of ROOc, are responsible of the Trp oxidation at low concentrations,while at high Trp concentrations, a mixture of peroxyl and alkoxyl radicals are involved in the oxidationof Trp residues.

AB - The oxidation of tryptophan (Trp) residues, mediated by peroxyl radicals (ROOc), follows a complexmechanism involving free radical intermediates, and short chain reactions. The reactivity of Trp towardsROOc should be strongly affected by its inclusion in peptides and proteins. To examine the latter, weinvestigated (by fluorescence) the kinetic of the consumption of free, peptide- and protein-Trp residuestowards AAPH (2,20-azobis(2-amidinopropane)dihydrochloride)-derived free radicals. Interestingly, theinitial consumption rates (Ri) were only slightly influenced by the inclusion of Trp in small peptides andproteins (human serum albumin and human superoxide dismutase). Depending on the Trpconcentration, the Ri versus Trp concentration ([Trp]) plots showed three regions. At low Trpconcentrations (1–10 mM), a linear dependence was observed between Ri and [Trp]; at intermediate Trpconcentrations (10–50 mM), the values of Ri were nearly constant; and at high Trp concentrations (50 mMto 1 mM), a slower increase of Ri than expected for chain reactions. Similar behavior was detected for allthree systems (free Trp, and Trp in peptides and proteins). For the first time we are showing that alkoxylradicals, formed from self-reaction of ROOc, are responsible of the Trp oxidation at low concentrations,while at high Trp concentrations, a mixture of peroxyl and alkoxyl radicals are involved in the oxidationof Trp residues.

U2 - 10.1039/C6RA12859A

DO - 10.1039/C6RA12859A

M3 - Journal article

VL - 6

SP - 57948

EP - 57955

JO - RSC Advances

JF - RSC Advances

SN - 2046-2069

IS - 63

ER -