Catalytic activity of a copper(II)-oxidized glutathione complex on aqueous superoxide ion dismutation

The study of the catalytic activity of a Cu(II)-oxidized glutathione system upon the disproportionation of superoxide radicals shows that the mononuclear complex MA catalyzes dismutation in the pH range 7-9. The corresponding first-order rate constant of value kcat congruent to 6 X 10(6) M-1 sec-1 is pH independent, whereas the second-order rate constant ks for the reference solutions is pH dependent. The kcat constant is about 10-, 100-, and 300-fold higher than the ks constant at pH 7, 8, and 9, respectively. The measured effect is explained in terms of free axial sites in the square-planar arrangement around the copper ion.