The objectives of the proposed research are to (1) monitor the zinc levels in liver and kidney metallothionein (MT) during prenatal and postnatal development in rats; (2) investigate the metabolism of radioactive MT (thionein) containing radioactive zinc, cadmium, mercury or copper; (3) determine the effects of stress on half-life of MT; (4) determine the influence of protein deficiency on tissue MT; (5) characterize a low molecular weight (MW) zinc binding ligand; and (6) characterize the copper and zinc containing proteins in the choroid plexus. Pregnant rats fed diets containing various levels of zinc or cadmium will be killed at different stages of pregnancy, and the MT levels and zinc content determined in the fetuses and liver and kidney of the dam. It is planned to isolate MT by gel filtration and DEAE cellulose chromatography and determine the zinc content by atomic absorption spectrophotometry. Subsequently, the influence of dietary zinc and cadmium on zinc and MT levels will be studied in liver and kidney of newborn, 4, 8, and 24 weeks-old rats. MT will be isolated from rats fed subtoxic levels of zinc, copper, cadmium or mercury and injected with 35S-cystine and the respective radioactive metals. These dual labeled MT preparations will be injected into rats, and the radioactivity determined in tissues and in cytosolic proteins to determine the influence of different metals on MT metabolism. The half-life of tissue (liver, kidney and pancreas) MT will be determined with use of 35S-cystine in rats placed in a cold room, heavily exercised, injected with CCl4, or fed various diets. Rats will be fed diets containing various levels of protein to determine the influence of protein status on MT levels and zinc metabolism. The low MW zinc binding ligand from kidney and the copper and zinc containing proteins from choroid plexus are planned to be purified by gel filtration and ion exchange resins and characterized.