The effect of cadmium on some oxygen-binding properties of the blood pigment of the lugworm Arenicola marina (annelida, polychaeta)

Abstract

The effect of cadmium was determined on some oxygen-binding characteristics (viz. oxygen affinity, subunit cooperativity, Bohr-effect and temperature effect) of the erythrocruorin of the lugworm, Arenicola marina. Oxygen affinity and subunit cooperativity were measured directly in the blood of Arenicola, both in blood collected from specimens kept under experimental conditions and from specimens obtained from their natural habitat. In the pH range of 7·3–7·8, which closely resembles in vivo blood pH values, cadmium does not affect the oxygen affinity at low concentrations (10 −8-10 −5 m), and decreases the O 2-affinity only slightly at higher concentrations (10 −5-2·10 −3 m). In the more alkaline pH range, the oxygen affinity increases considerably with increasing cadmium concentrations. Cadmium exerts a facilitating influence on the haem cooperativity at lowest concentrations (10 −8-10 −7 m) and a minor inhibiting influence at higher concentrations. The oxygen affinity, subunit cooperativity, the Bohr-effect and the temperature effect are pH dependent. The influence of cadmium on the magnitude of the Bohr-effect is pH-dependent. In vivo measurement of the oxygen affinity of Arenicola erythrocruorin gives evidence of a more pronounced inhibition of oxygen binding at increasing cadmium concentrations in the blood, compared with the effect on purified erythrocruorin solutions.