Mechanistic study of singlet oxygen formation by tryptophan and tyrosine peroxides in the context of damage to biomolecules by oxidants

Abstract

Damage to biomolecules (eg proteins) can be generated by extremely reactive oxidants, such as the hydroxyl radical (* OH), or by less reactive, and therefore more selective oxidants such as peroxyl, hypochlorous acid (HOCl) and oxygen radicals singlet (O2(1”g)). HOCl, for example, plays an important role in defense against pathogens. However, this same molecule is strongly related to the tissue damage that occurs in several inflammatory diseases. O2 (1”g) in turn is involved in the formation of lipid, DNA and protein hydroperoxides. These peroxides can react with metal ions, generating peroxyl and / or alkoxyl radicals, responsible, for example, for the propagation of lipid peroxidation and the generation of toxic compounds. The formation of O2 (1”g) has already been studied in lipoperoxidation processes, which occurs mainly through the mechanism discussed by Russell. Such a mechanism describes the interaction of peroxyl radicals with each other, generating an intermediate tetraoxide that decomposes generating as products an alcohol, a ketone and O2 (1”g).Proteins are considered the major targets for oxidants, due to the abundance in biological systems and the constant elevations of reactions with these reactive species. In addition, studies have shown that the decomposition of peroxides formed into proteins can result in subsequent damage to other proteins.Lipid hydroperoxides were proposed as likely sources of singlet oxygen in biological medium. However, it is unknown if peroxides of amino acids and proteins would also have the same capacity. It is known that the amino acids tryptophan and tyrosine are very susceptible to oxidation, and when reacting with singlet oxygen they generate stable peroxides. In this way, it is interesting to evaluate if the later reaction of these tryptophan and tyrosine peroxides with HOCl, are able to generate O2 (1”g), and to investigate the mechanism of the reactions. The objectives of this project include the elucidation of the products obtained from the photosensitization of tryptophan (W), tyrosine (Y) and N-acetyl tryptophan (NAcW); study of tryptophan reaction products incorporated into small peptides (HGWG-OH or H-GWG-OH) with oxidants O2 (1”g) and HOCl; using infrared luminescence detection and HPLC / MS / MS; study of the other reaction products formed in the reaction of hydroperoxides with HOCl by HPLC-MS-MS; perform NMR experiments to confirm the structures of the oxidized products.