Characterization studies on the cadmium-binding proteins from two species of New Zealand oysters

Two different types of New Zealand oysters - Ostrea lutaria (OL) and Crassostrea glomerata (CG) - contained different concentrations of zinc, copper, and cadmium. Both kinds of oysters were shown by gel filtration (G-75) to contain cadmium and zinc in fractions corresponding to a high molecular weight protein which was heat labile. OL oysters contained cadmium in fractions corresponding to a molecular weight of approximately 6500. The cadmium-binding protein in these fractions was heat-stable. This protein contained no detectable amounts of zinc and was not present in the CG oysters. CG oysters contained cadmium and zinc in a polypeptide with low molecular weight (MW 1000). The cadmium-binding oyster proteins are minimally reactive in a competitive binding radioimmunoassay in comparison to the reactivity of a typical vertebrate metallothionein; the proteins may be metallothioneins, but, if so, they do not exhibit the principal determinants characteristic of vertebrate metallothioneins