title: Mechanisms of flavonoid repair reactions with amino acid radicals in models of biological systems: a pulse radiolysis study in micelles and human serum albumin.
abstract: Neutral tryptophan (*Trp) and tyrosine (TyrO(*)) radicals are repaired by certain flavonoids in buffer, in micelles and in human serum albumin (HSA) with corresponding formation of semioxidized flavonoid radicals. In deaerated buffer, *Trp but not TyrO(*) radicals react with catechin. In micelles, quercetin and rutin repair both *Trp and TyrO(*) radicals. In addition to amino acid reactivity, microenvironmental factors and nature of the flavonoids govern this repair. Electron transfer efficiencies from quercetin to negatively charged *Trp radicals are 100% in the micellar pseudophases of positively charged cetyltrimethylammonium bromide, (CTAB), and neutral Triton X100 (TX100), but 55% in negatively charged sodium dodecyl sulfate (SDS). In oxygen-saturated CTAB micelles, quercetin also reacts with the superoxide radical anion. When bound to domain IIA of HSA, quercetin repairs, by intra- or intermolecular encounter, less than 20% of oxidative damage to HSA. Quercetin can also repair freely circulating oxidized molecules with repair efficiencies falling to 7% for oxidized *Trp, Tyr and alpha-MSH and to less than 2% for urate radical. This limited effectiveness is attributed both to the inaccessibility of bound quercetin and rutin toward radicals of circulating molecules and to the diffusion-controlled recombination of these radicals.
authors.affiliation: Centro de Metabolismo e Endocrinologia da Faculdade de Medicina de Lisboa, Portugal.
authors.forename: Paulo
authors.initials: P
authors.lastname: Filipe
authors.forename: Patrice
authors.initials: P
authors.lastname: Morlière
authors.forename: Larry K
authors.initials: LK
authors.lastname: Patterson
authors.forename: Gordon L
authors.initials: GL
authors.lastname: Hug
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Mazière
authors.forename: Cécile
authors.initials: C
authors.lastname: Mazière
authors.forename: João P
authors.initials: JP
authors.lastname: Freitas
authors.forename: Afonso
authors.initials: A
authors.lastname: Fernandes
authors.forename: René
authors.initials: R
authors.lastname: Santus
mesh_terms: D002392:Catechin / Q000737:chemistry; D004579:Electron Transport; D005419:Flavonoids / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008823:Micelles; D008954:Models, Biological; D010084:Oxidation-Reduction; D011675:Pulse Radiolysis; D011794:Quercetin / Q000737:chemistry; D012431:Rutin / Q000737:chemistry; D012709:Serum Albumin / Q000737:chemistry*; D014364:Tryptophan / Q000031:analogs & derivatives / Q000737:chemistry*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000737:chemistry*; D014527:Uric Acid / Q000737:chemistry; D000521:alpha-MSH / Q000737:chemistry
chemical_list: D005419:Flavonoids; D005609:Free Radicals; D008823:Micelles; D012709:Serum Albumin; D014527:Uric Acid; D014443:Tyrosine; D000521:alpha-MSH; D012431:Rutin; D014364:Tryptophan; D002392:Catechin; D011794:Quercetin