| Abstract: | The effect of cadmium (5 μ/ml) on the growth of Euglena gracilis is moderated by the addition of supplemental zinc levels above the normal 1 μ/ml level found in the growth medium. Gel chromatography reveals that th majority (ca. 85%) of cytosolic cadmium is localized in a cadmium-binding protein (CdBP). The CdBP appears to elute in a position slightly lower in molecular weight than mammalian metallothionein, contains thiol, and upon ion-exchange chromatography elutes in multiple peaks at ionic strengths greater than mammalian metallothioneins. The remaining cadmium is associated with high molecular weight components. Cytosolic zinc is found primarily (> 80%) in a low molecular weight peak distinct from cadmium, with the remainder as high molecular weight species. As the cells become zinc-deficient and cease proliferation, zinc is lost from the low molecular weight peak while, based on cytosolic protein, the zinc content of the high molecular weight peak remains essentially constant. |
