Suppression of Inhibitory Effects of Copper on Enzymatic Activities by Copper-Binding Substances from Athyrium yokoscense Assayed in vitro

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A metal-tolerant fern, Athyrium yokoscense, is capable of growing in highly copper-contaminated soil, but cupric chloride inhibited the activities of some enzymes extracted from the fern. The function in the detoxification of copper of two copper-binding substances was investigated by examination of their effects on various enzymes assayed in vitro, i.e. acid phosphatase (orthophosphoric-monoester phosphohydrolase [acid optimum], EC 3.1.3.2), glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP^+ 1-oxidoreductase, EC 1.1.1.49) and isocitrate dehydrogenase (threo-Ds-isocitrate: NADP^+ oxidoreductase [decarboxylating], EC 1.1.1.42). The two copper-binding substances, whose apparent molecular weights are 9.5 kDa and 2 kDa, were previously obtained from the soluble cytoplasmic fraction of the fern root. The 9.5-kDa substance, which is a cysteine-rich peptide induced as a result of exposure of the fern to copper, was found to suppress almost entirely the inhibitory effects of the metal on the enzymes. The suppressor activity of the peptide was nearly as effective as that of ethylenediaminetetraacetic acid. The 2-kDa substance, which is also found in fern that has not been exposed to copper, had a more modest suppressor activity. These results indicate that the 9.5-kDa substance may con-tribute to the copper-tolerance of the fern growing in copper-contaminated soil.
日本植物生理学会の論文