RESUMO
Gonyaulax polyedra is a marine unicellular algae that, together with other dinoflagellates, is responsible for most light emission in the ocean. In G. polyedra numerous processes are clockcontrolled, such as bioluminescence, that occurs during night phase, cell aggregation, photosynthesis that peak during the day and cell division that occurs at the transition between night and day. The activity of superoxide dismutase (SOD) in cell-free extracts of G. polyedra, carried out at different times of day and night, was found to be three to four times higher during the day. This rhythm continued in cells kept in constant light, indicating that the regulation can be attributed to the cellular circadian clock. Nondenaturating polyacrylamide gels reveal several SOD isoenzymes in G. polyedra, including CuZnSOD. Cyanide inhibits over 50 per cent of total SOD activity when added to the reaction mixture. Furthermore, G. polyedra SOD cross-reacts with polyclonal antibodies raised against SOD purified from erythrocytes (AbSOD) and over 50 per cent of its activity is inhibited by 25 muL of AbSOD. Although they are distant groups, such results suggest that algae and erythrocytes maintain high SOD structural homology. Besides gene regulation by reactive oxygen species concentration, G.polyedra SOD expression seems to be also under control of the biological clock.