Catalase and SOD (250 U/ml) were used to remove ROS suspected to affect the enzymatic activity for purified HAO incubated with A) O6BG, B) DACA, C) zaleplon, D) phthalazine E) BIBX1382, and F) zoniporide. No significant change in linearity of the enzyme was observed once these reagents were used, suggesting that ROS are not the reason for the decrease in enzymatic efficacy.