Cadmium-zinc interactions in the Ehrlich cell: metallothionein and other sites

Zinc and Cadmium metabolism in cultured Ehrlich cells has been studied. Under conditions of restriction of extracellular zinc by EDTA or chelex, zinc in basal Zn-metallothionein (Mt) is transferred from metallothionein to other sites with a rate constant of 0.35 hr-1. Current studies indicate that the rate constant for biodegradation of Mt protein is 0.07-0.11 hr-1, implying that Zn leaves the protein faster than it is biodegraded. After a 30 minute exposure of cells to 17 ng atoms Cd/mg cell protein, Cd initially displaces Zn from Mt and binds to high molecular weight species. Cell proliferation is markedly slowed, although the cells remain viable. Over time Cd shifts into newly synthesized Mt. This protein is made with an apparent rate constant four times that for basal Zn-Mt. The product contains equal amounts of Cd and Zn. However, cell proliferation is not restored for many hours after Cd is sequestered in Mt.