OXYGEN-DEPENDENT SULFIDE DETOXIFICATION IN THE LUGWORM ARENICOLA-MARINA

The lugworm Arenicola marina L. oxidizes entering sulfide to thiosulfate. After 8 h of normoxic incubations with sulfide concentrations of 0.2 to 1.0 mmol l-1 thiosulfate in the coelomic fluid amounted up to about 4 mmol l-1 whereas sulfite concentrations were 100-fold lower and no accumulation of sulfate in the coelomic fluid was found. The sulfide oxidation was highly oxygen dependent. An increase of oxygen partial pressure (P(O2)) in the medium was followed by enhanced thiosulfate production and by a decrease of sulfide concentration in the coelomic fluid. Under normoxia, the sulfide oxidation rate was sufficient to compensate the influx of sulfide into the coelomic fluid when the sulfide concentration in the medium was below 0.33 mmol l-1. When external sulfide was raised beyond this level, sulfide up to 5 mumol l-1 in the coelomic fluid appeared. Succinate in the body wall tissue was low as long as no sulfide appeared in the coelomic fluid, indicating the maintenance of an aerobic metabolism. The oxidation of sulfide to thiosulfate was localized in the mitochondria of the body wall tissue. The oxygen consumption of mitochondria was stimulated by the addition of sulfide. The mitochondrial sulfide oxidation rate depended on the amount of mitochondrial protein and followed a Michaelis-Menten kinetic. An apparent K(m) of 0.68 +/- 0.29 mumol l-1 and a V(max) of 41.9 +/- 22.3 nmol min-1 mg-1 protein was calculated. Sulfide was stoichiometrically oxidized to thiosulfate with 1 mol sulfide consuming 1 mol oxygen. Sulfide oxidation was not inhibited by sulfide concentrations as high as 100 mumol l-1. At low concentrations of cyanide or azide, when respiration without sulfide was already inhibited, sulfide oxidation could still be stimulated, tentatively indicating the existence of an alternative terminal oxidase. Specimens examined in the present study were collected near St. Pol de Leon, France, from 1989 to 1992.