Trp Oxidation by Copper-Ascorbate under Physiological Conditions

Tryptophan (Trp) is an essential amino acid which, beside its role in protein synthesis, is involved in a great diversity of biological functions (precursor of serotonine, of UV filters (Wood and Truscott, 1993)). In the field of the radical theory of aging, Trp is considered as a possible target of oxygen radicals. If occuring, in vivo Trp oxidation would not only affect these different functions but also produce highly reactive and toxic species. 3-OH-Kyn (hydroxy-kynurenine) and 3-OH-A A (hydroxy-anthranilic acid) have been reported to have a cataractogenic activity (Truscott and Martin, 1989; Tomoda et al., 1990; Truscott et al., 1991; Benavente and Truscott, 1991) in vitro by inducing protein cross-linking, and kynurenine derivatives are suspected to promote bladder carcinogenesis in mice and induce metal- mediated damages on DNA (Hiraku et al., 1995).