4-Aminoantipyrine (AAP) is scarcely administered as an analgesic drug because of side effects. The residue of MP in the environment is potentially harmful. To evaluate the toxicity of AAP from molecular level, the effects of AAP on the important antioxidant enzyme copper-zinc superoxide dismutase (Cu/ZnSOD) were explored using spectroscopic and molecular modeling methods. MP can spontaneously bind with Cu/ZnSOD with one binding site to form AAP-Cu/ZnSOD complex through hydrogen bond and van der Waals forces. The molecular docking simulation revealed that AAP bound into the Cu/ZnSOD interface of two subdomains, which induced some conformational and microenvironmental changes of Cu/ZnSOD and further caused the inhibition of Cu/ZnSOD activity. The present study provides important insights into toxic mechanism of AAP with Cu/ZnSOD. The estimated research route can be applied to characterize interactions of enzyme systems and other pollutants and drugs. (C) 2013 Elsevier B.V. All rights reserved.