When S. pombe is cultured in a medium containing a high concentration of CdCl2 (1 mM), it grows for over 20 h accumulating Cd2+ in the cells. Simultaneously, Cd-binding peptides (Cd-BP1 and -BP2) are synthesized, and accumulated depending on the time after addition of Cd2+ to the culture medium. Apparent molecular weights of Cd-BP1 and -BP2 are 4,000 and 1,800, respectively. Both Cd-BPs are composed of common unit peptides, confirmed by chemical and physicochemical analyses.

Two kinds of Cd-binding peptides (Cd-BP1 and Cd-BP2) are induced in fission yeast upon addition of CdCl2 to the culture medium (l). It was also reported that Cd-BP1 and Cd-BP2 consisted of the same components, unit peptides (Cys3, Glu3, Gly1) and Cd atoms, though the respective amounts of components in each molecule were different (1, 2). Now, we have found that Cd-BP1 contains about 1 mol of acid-labile sulfide per mol, and Cd-BP2 contains no labile sulfide. The existence of the labile sulfide explains the unique physicochemical characteristics of Cd-BP1. Since acid-labile sulfide has not been found in metallothioneins or other metallothionein-like metal-binding proteins, the occurrence of labile sulfide in Cd-BP1 is the first instance in this field.

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Osmotic stress hampers the growth of Saccharomyces cerevisiae, and this effect is mediated by oxidative stress. A simple test for the biological evaluation of antioxidants was developed on the basis of recovery of growth delay of Cu, Zn-superoxide dismutase-lacking yeast (SOD1Δ) under hyperosmosis. The SOD1Δ strain suffered from growth inhibition in a medium containing 1.7 M sorbitol. Protein oxidation in SOD1Δ cells was greatly increased by exposure to a hypertonic medium, indicating the accumulation of reactive oxygen species followed by oxidation of cellular materials. The hyperosmosis-induced growth arrest of SOD1Δ was abolished by the addition of L-ascorbic acid to the medium; the antioxidant effect depended on the concentration, ranging from 1 to 10 mM. Cysteine, N-acetyl-cysteine, and glutathione were also able to restore the growth of SOD1Δ cells. High concentrations of these thiol compounds proved less effective, probably due to adverse effects of an excess of these antioxidants. No growth restoration was seen for typical polyphenol antioxidants, including curcumin, quercetin and catechin.

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