DNA- and protein-scission activities of ascorbate in the presence of copper ion and a copper-peptide complex.

L-Ascorbic acid, when combined with either copper(II) ion or a copper(II)-tripeptide complex, extensively cleaved several viral DNAs and proteins under in vitro conditions. Neither ascorbate nor copper tripeptide (Cu2+-diglycyl-L-histidine) alone caused any apparent changes on these molecules. Various transition metal ions and reducing agents were examined under comparable conditions to determine the basic requirements for both DNA degradation and protein scission activities. Copper and iron are the two most effective transition metal ions examined that exhibit these activities in the presence of ascorbate. The addition of catalase, but not superoxide dismutase, can partially inhibit the scission of DNA in vitro, suggesting that H2O2 may be involved in these activities. Among the various reducing agents tested, ascorbate was most effective in causing DNA scission and protein cleavage, corroborating the possible role of H2O2 in the cleavage reactions. One of the products of the reactions of copper/ascorbate is probably the hydroxyl radical generated from H2O2, which can be formed from the oxidation of ascorbate.