Isolation and some properties of copper-binding proteins found in a copper-resistant strain of yeast

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Abstract
Copper-binding proteins were extracted from a copper-resistant strain of Saccharomyces cerevisiae which was obtained by repeated subculturing in a copper-containing medium. They were separated into three types through purification steps such as salt fractionation, gel filtration and preparative polyacrylamide gel electrophoresis. They resembled each other in amino acid composition. Acidic amino acids, lysine, serine, glycine and half-cystine constituted a large part of the protein, with a small amount of hydrophobic amino acids. Aromatic amino acids and methionine were almost absent. The molecular weight of the components was estimated to be about 10,000 by Sephadex gel filtration and electrophoresis on polyacrylamide gel (slope method). Absorption spectra of the components exhibited a broad band at 275 nm, but none in the visible region, thus resembling that of copper-thionein. Moreover, the absorption band at 275 nm changed markedly on addition of Ag+, Hg2+, CN− or H2O2, which are well known as thiol reagents. These components were abo produced in the parent cells, if they could grow in a copper-containing medium. Based the results of experiments using various culture conditions and some other yeast species, a possible role of the components is discussed.

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