Mechanism of copper-catalyzed autoxidation of cysteine.
The kinetics of copper-catalyzed autoxidation of cysteine and its derivatives were investigated using oxygen consumption, spectroscopy and hydroxyl radical detection by fluorescence of a coumarin probe. The process has complex two-phase kinetics. During the first phase a stoichiometric amount of oxygen (0.25 moles per mole of thiol) is consumed without production of hydroxyl radicals. In the second reaction phase excess oxygen is consumed in a hydrogen peroxide-mediated process with significant *OH production. The reaction rate in the second phase is decreased for cysteine derivatives with a free aminogroup and increased for compounds with a modified aminogroup. The kinetic data suggest the catalytic action of copper in the form of a cysteine complex. The reaction mechanism consists of two simultaneous reactions (superoxide-dependent and peroxide-dependent) in the first phase, and peroxide-dependent in the second phase. The second reaction phase begins after oxidation of free thiol. This consists of a Fenton-type reaction between cuprous-cysteinyl complex and following oxidation of cysteinyl radical to sulfonate with the consumption of excessive oxygen and significant production of hydroxyl radicals.
Kachur
A V
AV
Department of Radiation Oncology, School of Medicine, University of Pennsylvania, Philadelphia 19104-6072, USA. kachur@mail.med.upenn.edu
Koch
C J
CJ
Biaglow
J E
JE
D002374:Catalase / Q000494:pharmacology; D003300:Copper / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry*; D005978:Glutathione / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D013482:Superoxide Dismutase / Q000494:pharmacology
D017665:Hydroxyl Radical; D003300:Copper; D002374:Catalase; D013482:Superoxide Dismutase; D005978:Glutathione; D003545:Cysteine; D010100:Oxygen