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Nitric Oxide Inhibition of Tobacco Catalase and Ascorbate Peroxidase

We used a variety of nitric oxide (NO) donors to demonstrate that NO inhibits the activities of tobacco catalase and ascorbate peroxidase (APX). This inhibition appears to be reversible because removal of the NO donor led to a significant recovery of enzymatic activity. In contrast, APX and catalase were irreversibly inhibited by peroxynitrite. The ability of NO and peroxynitrite to inhibit the two major H₂O₂-scavenging enzymes in plant cells suggests that NO may participate in redox signaling during the activation of defense responses following pathogen attack.