Reversibility of copper-thiol binding in Nitzschia closterium and Chlorella pyrenoidosa

Abstract

The effect of ionic copper and copper complexes on intracellular thiols in the marine diatom Nitzschia closterium (Ehrenberg) W. Smith, and the green alga Chlorella pyrenoidosa Chick was studied using the lipid-soluble thiol reagent, dithiodipyridine. Treatment of cells with copper ions significantly reduced the concentration of intracellular thiol groups, whereas copper complexes and H 2O 2 had no effect. To test the reversibility of intracellular copper-thiol binding in N. closterium and C. pyrenoidosa, cells exposed to copper (60–200 μg Cu·1 −1) were treated with various sulfhydryl compounds and chelating agents, with and without removal of copper from solution. Cysteine, glutathione (GSH), EDTA and bathocuproine disulfonate were most effective in reversing copper toxicity, whereas oxidized glutathione, cystine and glycine had no effect. It is proposed that copper (II) adsorbed to the algae is reduced to copper (I) by -SH groups, and bound as a Cu(I)-S-complex. Sulfhydryl compounds can reverse toxicity through thiol-disulfide interchange reactions, allowing algal growth to recommence, and powerful copper-chelating agents produce the same effect by withdrawing copper from the cell.