Lorrain et al. Free Radical Biol. Med. 2010

Metmyoglobin (MbFe), a major form of dietary iron, is an efficient inducer of lipid and protein oxidation. Indeed, MbFe is able to cleave hydrogen peroxide and lipid hydroperoxides with subsequent formation of ferrylmyoglobin (MbFe=O) and lipid oxyl and peroxyl radicals. In the first part of this work, the mechanism of the reaction between MbFe and H2O2 is revisited with an emphasis on the influence of bovine serum albumin (BSA). BSA does not affect the rate of MbFe=O formation but inhibits the formation of the redox-inactive green pigment (heme-protein cross-link species). Although tightly bound to BSA, the flavonol quercetin is still able to reduce MbFe=O as a likely result of long-range electron transfers within a protein-protein complex. In a second part, BSA is shown to strongly slow down the metmyoglobin-catalyzed consumption of linoleic acid hydroperoxides with formation of ketones as the main products. In the process, only low concentrations of ferrylmyoglobin are slowly accumulated. A catalytic mechanism is proposed that involves a one-electron oxidized metmyoglobin species distinct from ferrylmyoglobin.