![]() This study suggests that the conformation changes of two key antioxidant enzymes, catalase and superoxide dismutase, and the dissolution of AgNPs depended on the protein structure and could result in different degrees of enzymatic activity modulation. Therefore, studies related to the impact of silver nanoparticles (AgNPs) on the structure and function of antioxidant enzymes at the molecular level are crucial for a comprehensive evaluation of their toxicity. Environmental significance Excessive production of reactive oxygen species in cells by direct interaction with particles and/or dissolved species is currently accepted as one of the main mechanisms of cellular toxicity of engineered nanoparticles. Overall, the results showed that the changes in the protein conformation and the dissolution of AgNPs depended on the protein structure and could result in different degrees of enzymatic activity modulation. By contrast, the formation of the AgNP–SOD complex has only a marginal influence on the protein conformation and has no impact on its metallic cofactors, and thus its enzymatic activity. Instead, our results suggest that the formation of the AgNP–CAT complex induced conformation changes in the CAT, which resulted in an impairment of its enzymatic activity together with Ag( I) adsorption. Only CAT was able to promote AgNP dissolution, without the impact of the released Ag ions on its heme cofactor. Both enzymes interacted with AgNPs by forming surface complexes. By using a combination of spectroscopic, imaging and fractionation techniques, we explored the interactions between citrate-coated AgNPs (20 nm) and two key antioxidant enzymes: catalase (CAT) and superoxide dismutase (SOD). Therefore, mechanistic studies related to the impact of AgNPs on the structure and function of antioxidant enzymes at the molecular level are essential for a comprehensive evaluation of their toxicity. Oxidative stress is accepted as a key mechanism of silver nanoparticle (AgNP) toxicity in living organisms.
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