Kinetic Studies on the Role of Dioxygen in the Cooper-Catalyzed Autoxidation of Cysteine

Article abstract of DOI:10.1246/bcsj.68.831

Kinetic studies on a role of dioxygen in the copper-catalyzed autoxidation of cysteine in glycylglycine-phosphate buffers have been carried out.The rate of autoxidation was obtained by measuring the consumption of cysteine.It has been revealed that cysteine is oxidized by a "sequential mechanism".The reaction pathway can be shown by Eqs. 1, 2, 3, and 4; cysteine is oxidized not only by copper(II) species, but also by copper(I)-O2 adducts: Cu(II)-L + CyS^- = L-Cu(II)-CyS^- (1) L-Cu(II)-CyS^- -> Cu(I)-L + CyS^radical (2) Cu(I)-L + O2 = L-Cu(I)-O2 (3) L-Cu(I)-O2 + Cy S^- + 2H⁺ -> Cu(II)-L + CyS^radical + H2O2 (4) Here, L represents ligands including cysteine.The oxidation step (4) catalyzed by the Cu(I)-O2 species was proposed to be rate-determining.