Determination of the superoxide dismutase-like activity of cimetidine-Cu(II) complexes.

Using the direct method of pulse radiolysis to determine the superoxide dismutase like activity of copper(II) cimetidine complexes, it was found that the reaction rate constant with O2-, kcat, was (8.5 +/- 0.5) x 10(8) M-1s-1 independent of the cimetidine concentrations present in excess of 50-200 microM over the metal. The results suggest that either the 1:1 ligand to metal complex does not catalyze O2- dismutation at a comparable rate to that of the 2:1 complex, or that the stability constant of the last species is much higher than that determined earlier by Kimura et al., and only the 2:1 species is present in the solutions. With the indirect methods of cytochrome c and NBT for determining the ability of these complexes to catalyze O2 dismutation, these compounds exhibited a much lower SOD activity, and kcat was determined to be (5.0 +/- 0.3) x 10(6) and (7.6 +/- 0.4) x 10(7) M-1s-1, respectively using the two assays.