Impact of anoxia and hydrogen sulphide on the metabolism of Arctica islandica L. (Bivalvia)

Abstract

The effects of environmental anoxia and anoxic sulphide exposure on metabolism are measured in tissues of the clam, Arctica islandica. Under anoxia the total activity of glycogen phosphorylase and the percentage of the enzyme in the active a form are significantly reduced. Alterations in pyruvate kinase kinetics produce slightly increased V max values, strongly increased S 0.5 PEP, slightly increased S 0.5 ADP in the muscular tissues and mantle, and strongly reduced I 50 for alanine (up to 90-fold increased sensitivity). Anoxia also stimulates a reduction of fructose-2,6-bisphosphate levels, an effector of phosphofructokinase, in all tissues tested. These effects are consistent with enzyme modifications induced by phosphorylation to produce a restricted activity. Anoxic sulphide exposure produced similar effects on the glycogenolytic enzyme glycogen phosphorylase (GP), as does anoxia alone. In the course of the experiments, mitochondrial energy metabolism is not affected by sulphide. The accumulation of the anaerobic indicator metabolite succinate is almost identical in adductor and foot under both stresses. The data suggest a similar coordinated metabolic rate control under environmental anoxia and anoxic sulphide exposure, i.e. H 2S has no distinctly different effects on the parameters tested. This study provides evidence that while being burrowed in anoxic sediments, the clams are able to withstand the detrimental effects of sulphide for a substantial period of time.