STORAGE OF SOLAR-ENERGY BY PRODUCTION OF HYDROGEN-PEROXIDE BY THE BLUE-GREEN-ALGA ANACYSTIS-NIDULANS R2 - STIMULATION BY AZIDE

The production of hydrogen peroxide by Anacystis nidulans R2 in the presence of methyl viologen occurs by using the redox power from water promoted by the photosystems of the blue-green alga. Thus, in the presence of the photosynthetic inhibitor DCMU or in the dark, H2O2 production does not take place. In cells permeabilized with lysozyme, the addition of ionophores, which is expected to increase the electron flow, produces only a small increase to initial velocity of hydrogen peroxide production. On the other hand, in nonpermeabilized cells, the addition of superoxide dismutase increases the initial velocity of hydrogen peroxide production, but the net amount accumulated by the system is very low because of posterior decomposition. Preincubation of cells with azide, which inhibits the catalase, prevents the decomposition, thereby increasing drastically the amount of hydrogen peroxide accumulated by the system after a few hours. Hence, H2O2 production appears to be limited mainly because of decomposition by catalase activity rather than by the photosynthetic electron flow rate or the diffusion of products through the cell wall. The net production of hydrogen peroxide by the system was enhanced severalfold by treatment with azide. If one takes into account the use of hydrogen peroxide as fuel due to the large amount of energy released in its dismutation, the photosystem can be a useful tool in the storage of solar energy.