Copper-release from yeast Cu(I)-thionein by hypothiocyanite (OSCN-)

In the course of an oxidative burst oxygen free radicals and hypothiocyanite (OSCN-), a transiently abundant derivative of thiocyanate (SCN-), are formed in the presence of activated polymorphonuclear leukocytes (PMNs). At the same time Cu(I)-thionein is present and the question arose whether or not thiocyanate and its oxidized form may transiently release highly Fenton active copper to improve the efficacy of the above mentioned oxidative burst. Thus, the reaction of yeast Cu-thionein with OSCN- was examined. Indeed, a release of copper from the Cu(I)-thiolate clusters of the protein was observed ex vivo. Both the chiroptic and luminescence emission signals of Cu-thionein essentially levelled off in the presence of a 15-fold molar excess of OSCN- expressed per equivalent of thionein-copper. The effective copper-releasing activity of this reagent was confirmed by equilibrium dialysis. The demetallized protein could be reconstituted under reductive conditions. SCN- did not affect the copper-thiolate bonding. It rather acts as a potent metabolic source for the transient copper release from Cu-thionein in the presence of activated PMNs.