| Abstract
| - Selective oxidative damage to apolipoprotein B in LDL can be effected radiolytically by •Br2-radicals. Twenty-seven Trp residues constitute major primary sites of oxidation, but two-thirds of oxidizedTrps (•Trp) that are formed are repaired by intramolecular electron transfer from Tyr residues with formationof phenoxyl radicals (TyrO•). Analysis of •Trp and TyrO• transient absorbance changes suggests thatother apolipoprotein B residues, probably Cys, are oxidized. LDL-bound quercetin can efficiently repairthis damage. Absorption studies show that a LDL particle has the capacity to bind ∼10 quercetin moleculesthrough interaction with apolipoprotein B. The repair occurs by intramolecular electron transfer characterizedby a rate constant of 2 × 103 s-1. In contrast, rutin, a related flavonoid which does not bind to LDL,cannot repair oxidized apolipoprotein B. Urate is a hydrophilic plasma antioxidant which displays synergisticantioxidant properties with flavonoids. Urate radicals produced by •Br2- can also be repaired by LDL-bound quercetin. This repair occurs with a reaction rate constant of 6.8 × 107 M-1 s-1. Comparison withprevious studies conducted with human serum albumin-bound quercetin suggests that quercetin analoguestailored to be carried preferentially by lipoproteins might be more powerful plasma antioxidants thannatural quercetin carried by serum albumin.
|
