Photoreduction of 18O2 and H218O2 with concomitant evolution of 16O2 in intact spinach chloroplasts

Abstract

Illuminated intact spinach chloroplasts decomposed one molecule of H218O2 which resulted in the evolution of a half molecule of 16O2, but little 18O2. The chloroplasts showed the same rate of photoreduction of 18C2 as that of the evolution of 16O2 without accumulation of H218O2. These reactions were suppressed by DCMU, and also by several inhibitors of ascorbate peroxidase and dehydroascorbate and monodehydroascorbate reductases in chloroplasts. These observations indicate that the hydrogen peroxide produced in chloroplasts is reduced to water by a peroxidase using a photoreductant as the electron donor. The hydrogen peroxide scavenging system of chloroplasts was inactivated if hydrogen peroxide was added in the dark, but not if added during the light. Show more