Recombinant stromal APX defective in the unique loop region showed improved tolerance to hydrogen peroxide.

Ascorbate peroxidase (APX) of chloroplasts plays a pivotal role in detoxifying the hydrogen peroxide (H2O2) produced through photoexcitation of the photosystem, but it easily loses its catalytic activity under attack by excess H2O2. Here we report that the H2O2-tolerance of APX localized in the stroma of chloroplasts was improved by removing a unique 16-amino-acid-residue loop not found in H2O2-tolerant isoforms of cytosol and glyoxysome.