Cadmium-binding protein in a cadmium-resistant strain of Saccharomyces cerevisiae.

A Cd-binding protein in the Cd2+-resistant strain 301N of Saccharomyces cerevisiae was induced by administration to 0.5 mM CdSO4. The protein was purified by a gel-permeation and subsequent ion-exchange column chromatographies. The purified Cd-binding protein had the characteristics of metallothioneins: (1) low molecular weight (9.0 kDa), (2) high Cd content (63 micrograms/mg protein), (3) amino-acid composition rich in cysteine (18%), basic and acidic amino acids and free from aromatic amino acids, and (4) an absorption shoulder at near 250 nm. Acid pH or EDTA treatments abolished 250 nm absorption of the Cd-binding protein, and the formed apoprotein was capable of binding Cd2+, Cu2+ and Zn2+, respectively. Heat treatment (75 degrees C) little affected the ultraviolet absorption or sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of Cd-binding protein. These results suggest that metallothionein generally found in animals also occurs in Cd-adapted yeast cells and thus has a role in its Cd-resistance.