Biological function of metallothionein: I. Synthesis and degradation of rat liver metallothionein

Abstract

The synthesis and degradation of rat liver metallothionein (MT) were investigated using 14C-cystine as precursor, Cd to stimulate the synthesis of this protein, and Sephadex G-75 chromatography as an isolation method. Incorporation of 14C-cystine into MT was normally low, but was greatly stimulated by s.c. Cd injection which also caused a temporary, but great, accumulation of Zn in MT fraction. A biological half-life of 4.2 days was found for liver MT. A second dose of Cd given after ip 14C-cystine injection prolonged only slightly the half-life (4.9 days). While Cd in the MT fraction remained at a constant level, Zn disappeared from this fraction at a rate similar to that of 14C-labeled MT, indicating the involvement of MT in Zn metabolism. This was further indicated by the stimulatory effect of s.c. Zn injection on the incorporation of 14C-cystine into MT. This stimulatory effect was also shared by s.c. injection of Cu and Hg. Further purification of MT fraction obtained by Sephadex G-75 chromatography on a DEAE-cellulose column revealed two MT peaks which contained more than 90% of the 14C, Cd and Zn put on the column, and high sulfhydryl groups ( 13.9 and 14.0-SH 10,000 MW , respectively). This verified that 14C-cystine was indeed incorporated into MT and that Sephadex G-75 chromatography was an adequate separation technique for isolation of MT for the present study.