Respiratory pigments of Yoldia eightsi, an antarctic bivalve

Yoldia eightsi, an infaunal protobranch bivalve inhabiting the soft sediments of the Antarctic Sea, contains hemocyanin in its hemolymph and an intracellular hemoglobin in its gills. The concentration of hemocyanin in the hemolymph of Y. eightsi is very low, but the presence of this protein was documented by transmission electron microscopy after negative staining. The structure of Y. eightsi hemocyanin appears to be remarkably similar to that found in Gastropoda. The intracellular gill hemoglobin can be recovered after osmotic shock of the tissue and is isolated as a monomeric form, the molecular weight of which is 15.7 +/- 0.4 kDa, as detected by FPLC gel-filtration experiments and SDS-PAGE. Isoelectric focusing experiments suggest the presence of a single native component with pI 6.6. Aggregation products accumulate during exposure to air and are resistant to SDS and beta-mercaptoethanol treatment. This process can be avoided by maintaining the sample under a CO atmosphere. The oxygen dissociation curves, determined at pH 7.0 and 7 degrees C, are slightly sigmoidal, giving a Hill constant value of 1.35, probably related to the formation of aggregation products. The affinity for oxygen is moderately high, half saturation occurring at 3.15 mmHg.