BIOCHEMICAL ADAPTATIONS OF NEREIS-DIVERSICOLOR (POLYCHAETA) TO TEMPORARILY INCREASED HYDROGEN-PEROXIDE LEVELS IN INTERTIDAL SANDFLATS

Toxic hydrogen peroxide (H2O2) is photochemically generated in hyperox ic and normoxic intertidal pools. Surprisingly high amounts of H2O2 pe netrate the redoxcline, and are measurable in pore water in spite of t he anoxic conditions prevailing there. Bioturbate macrofauna inhabitin g these sediments encounters oxic conditions with peroxide in surface pools and anoxic conditions with peroxide in the sediment. We studied antioxidative properties in the polychaete Nereis diversicolor. Antiox idant enzyme activities of catalase and superoxide dismutase (SOD) sho wed annual variations correlated to the environmental peroxide concent rations. Epitokous specimens from April exhibited very high enzyme act ivities. Catalase was predominantly localised in the mitochondria and is inducible by peroxide incubation under experimental conditions. SOD activities were not inducible during oxic peroxide incubation. In con trast, SOD had higher activities when the worms were kept anoxically i n the presence of hydrogen sulfide (100 muM) or hydrogen peroxide (5 m uM). The radical stress the worms encountered during anoxic peroxide i ncubation was reflected by a highly increased lactate formation. Under oxic conditions 500 nM H2O2 decreased oxygen uptake of N. diversicolo r by 38 %. In epitokous N. diversicolor, this was accompanied by a con version of heme to the green pigment biliverdin, a potent antioxidant. Biliverdin Wds accumulated by the worms during oogenesis under natura l conditions. Therefore its formation during spawning seems to be a re sponse to increasing hydrogen peroxide concentrations in sediment pore water during spring. Biliverdin was not formed under anoxic condition s, because the conversion requires oxygen. Atokous worms lacked the ab ility to form biliverdin when exposed to peroxide.