Determination of the Superoxide Dismutase-Like Activity of Cimetidine-Cu(II) Complexes

Abstract

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.

Key Words:

• SOD
• Cimetidine
• Copper
• O⁻₂
• pulse radiolysis.