[Oxidation of orcinol by ceruloplasmin and mixed-ligand copper complexes]

Unable to oxidize orcinol (3,5-dihydroxytoluene) under conventional conditions, ceruloplasmin (Cp) catalyzes its oxidation when superoxide radicals are injected into the solution with the aid of a high-voltage generator. The O2-. to oxidized orcinol ratio in solution is close to 2:1. The concentration of hydrogen peroxide, which is the product of the Cp-catalyzed dismutase reaction, is about half that of O2-. No slower than by the native enzyme, orcinol in the presence of O2-. is oxidized by Cp depleted of all its type 2 coppers and partly of type 1 Cu2+. Copper complexes with oxalate and pyrophosphate are able to oxidize orcinol under aerobic conditions, one molecule of oxygen being consumed per each oxidized molecule of orcinol. Both the oxidation of orcinol by Cp and by copper complexes are inhibited by cyanide. Orcinol oxidation seems to be caused by singlet oxygen produced in the Cp-catalyzed dismutase reaction.