Biological function of metallothionein-IV. Biosynthesis and degradation of liver and kidney metallothionein in rats fed diets containing zinc or cadmium.

The half-lives of liver and kidney metallothionein of rats fed diets containing either 2,000 ppm Zn or 100 ppm Cd were determined by a single injection of 14C-cystine. This protein was purified by Sephadex G-75 and DEAE cellulose column chromatography. Half-lives of liver metallothionein in rats fed the basal (18 ppm Zn), high Zn (2,000 ppm Zn), high Zn then basal, and high Cd (100 ppm) diet were, respectively, 3.4, 2.7 1.3, and 3.3 days, and that of kidney metallothionein were, respectively, 2.0, 2.2, 1.4, and 3.6 days. Thus, Cd-thionein has a longer half-life than Zn-thionein in both liver and kidney. The major species of metallothionein, which were separated on DEAE cellulose, had similar half-lives. Metallothionein, a protein having high content of metals and relatively short half-life, is possibly involved in cellular regulatory function.