Studies on Cd-binding proteins in short-necked clam.

In this study, short-necked clams were exposed to Cd-containing sea water for the following stages: Stage L: exposed in 0.1 ppm Cd for 22 days, Stage Sa: exposed in 0.1 ppm Cd for 10 days, Stage Sb: kept in natural sea water for 10 days after Stage Sa, Stage Sc: re-exposed in 0.1 ppm Cd for 10 days after Stage Sb. The supernatant liquid containing water-soluble Cd-binding proteins (Cd-BP) was obtained from the homogenate of the sample at each stage. In order to estimate the molecular weights and the behavior of Cd-BP, the supernatants were fractionated by Sephadex G-50 gel chromatography. It was found that Cd in the clam combined dominantly with the proteins in peaks A (M. W. more than 30, 000), B (M. W. 22, 000±7, 000), and C (M. W. 8, 000-2, 500). We conclude that Cd in the clam is combined chiefly with Cd-BP in peak A for short period exposures, but as the exposure period becomes longer, the Cd-BP in peak B acquires the leading role in intaking Cd. The remarkable behavior of the clam must be due to the induction of a synthesis of Cd-BP.