PEROXIDATION OF MODEL LIPOPROTEIN SOLUTIONS SENSITIZED BY PHOTOREDUCTION OF FERRITIN BY 365-NM RADIATION

A mechanistic study involving the 365 nm irradiation of aerated, phosp hate-buffered solutions of human high-density lipoproteins (HDL(3) fra ction) and ferritin was undertaken. The 365 nm irradiation of phosphat e-buffered horse spleen ferritin solutions induces the release of Fe2 in the medium. The initial quantum yield of Fe2+ release on irradiati on is 0.002. This quantum yield is oxygen independent. The 365 nm irra diation of mixtures of HDL and ferritin leads to alterations in apolip oproteins as revealed by tryptophan (Trp) oxidation and electrophoreti c pattern modification. In parallel with protein damage, lipid peroxid ation is induced as shown by hydroperoxide and thiobarbituric acid rea ctive substances (TBARS) formation. These peroxidations are strongly r educed in 0.1 M formate solution, which suggests chain initiation by ( OH)-O-. radicals or subsequent radicals produced by (OH)-O-.. They are completely inhibited by desferrioxamine, consistent with propagation by Fe2+ ion. By contrast, incubation of HDL in the presence of ferriti n and FeSO4 induces only poor auto-oxidation. The biological relevance of this study is discussed.