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 O^-₂, k_cat, was (8.5 ± 0.5) × 10⁸ M^-1s^-1 independent of the cimetidine concentrations present in excess of 50-200 μM over the metal. The results suggest that either the 1: 1 ligand to metal complex does not catalyze O^-₂ 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 el al.,¹ 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 O^-₂ dismutation, these compounds exhibited a much lower SOD activity. and k_cat was determined to be (5.0 ± 0.3) × 10⁶ and (7.± 0.4) × 10¹ M^-1s^-1. respectively using the two assays.