Hydrogen peroxide generation in organelles of Euglena gracilis

Hydrogen peroxide (H2O2) generation in intact mitochondria and chloroplasts was investigated in Euglena gracilis. In mitochondria, the addition of respiratory substrate caused the formation of H2O2. Lactate, the most effective substrate, yielded H2O2 at the rate of 9.5 nmol min−1 mg protein−1. Chloroplasts showed a rate of H2O2 generation of 5 μmol mg chlorophyll−1 hr−1 under illumination. The results reported here demonstrate that H2O2 is generated in mitochondria and chloroplasts and immediately diffuses from each organelle into the cytosol.