A pulse radiolytic study on the reaction of hydroxyl and superoxide radicals with yeast Cu(I)-thionein.

In a pulse radiolytic study employing aqueous intact yeast copper(I)-thionein at pH 7 it was shown that both superoxide and hydroxyl radicals efficiently react with this Cu(I)- and thiolate-rich protein. The reaction constant of hydroxyl radicals with Cu(I)-thionein was determined by competition kinetics and was 2.2 x 10(11) M-1 s-1 at a rate close to a diffusion-controlled limit. The reaction of Cu(I)-thionein with superoxide was also successful and proceeded at a rate of 7.5 x 10(6) M-1 s-1. According to chiroptical and luminescence emission measurements minor oxidation of the copper(I)-thiolate oligonuclear binding centres was observed, leading to the release of some Cu(II). It is important to realise the dual reactivity of this yeast Cu(I)-thiolate protein in controlling copper transport and storage as well as its distinct role in the scavenging of free radicals.