Radical scavenging properties of tryptophan metabolites. Estimation of their radical reactivity.
Radical scavenging properties of tryptophan metabolites were estimated using their radical reactivity. Metabolites of the kynurenine and the melatonin biosynthesis pathway were mainly examined by use of a kinetical model. Their radical reactivity was determined as the reaction rate constant with a stable free radical, such as galvinoxyl; that is a phenoxy radical. The rate constants of the metabolites have a widely ranged spectrum, which can be divided into three groups. The first group (3-hydroxykynurenine, 3-hydroxyanthranilic acid, and indole-3-pyruvic acid) is more reactive than alpha-tocopherol; the reactivity of the second group (xanthurenic acid, serotonin, N-acetylserotonin) is similar to that of butylated hydroxytoluene (BHT); the third group (kynurenic acid, melatonin, and other ones) is less reactive than BHT.