Evidence for an inducible cadmium binding protein metallothionein in chick embryo

Abstract

Cadmium binding protein metallothionein was isolated in a partially purified form from the liver of cadmium treated chick embryos. This binding protein was totally absent in normal chick embryo, though the induction occurred with cadmium exposure in the embryonic liver. Incorporation studies with 3H-leucine or 3H-lysine indicated the active synthesis of metallothionein after 10 hrs of cadmium injection. Since the characteristic of metallothionein is by its metal content, we estimated the cadmium concentration in all fractions and it was evident that cadmium peak corresponded only with the peak of radioactive amino acid incorporation to metallothionein. This result suggests that binding protein is specific for cadmium. Further experiments have been conducted with actinomycin D treatment to cadmium treated embryo to understand the mechanism of metallothionein induction. The incorporation of 3H-leucine into hepatic metallothionein of cadmium exposed embryos was not inhibited by actinomycin D treatment. suggesting that cadmium does not act at the level of transcription in the metallothionein biosynthesis, occurred in chick embryo.