Scavenging of Hydrogen Peroxide in Prokaryotic and Eukaryotic Algae: Acquisition of Ascorbate Peroxidase during the Evolution of Cyanobacteria

Ascorbate (AsA) peroxidase was found in six species of cyanobacteria among ten species tested. Upon the addition of H218O2 to the cells of AsA peroxidase-containing cyanobacteria, 16O2 derived from water and 18O2 derived from H2I8O2 were evolved in the light. The evolution of 16O2 was inhibited by DCMU and did not occur in the dark, but I8O2 was evolved even in the dark or in the presence of DCMU. Similar light-dependent evolution of 16O2 was observed in the cells of AsA peroxidase-containing Euglena and Chlamydomonas. However, the cells of AsA perox-idase-lacking cyanobacteria evolved only 18O2 in either the light or dark. Furthermore, the quenching of chlorophyll fluorescence induced by hydrogen peroxide was observed only in the cells of the AsA peroxidase-containing Synechocystis 6803, and not in the cells of Anacystis nidulans which lacks AsA peroxidase. Thus, cyanobacteria can be divided into two groups, those that has and those that lacks AsA peroxidase. The first group scavenges hydrogen peroxide with the peroxidase using a photoreductant as the electron donor, and the second group only scavenges hydrogen peroxide with catalase.