Studies on the interaction of cupric isonicotinohydrazide with DNA

The interaction of cupric isonicotinohydrazide (Cu/sup II/INH), antiviral compound, with calf thymus DNA was investigated by circular dichroism (CD) and nuclear magnetic resonance (NMR). Gel electrophoresis of DNA incubated with Cu/sup II/INH showed cleavage of DNA to various extents. This cleavage was found to be time and concentration dependent. In the presence of Cu/sup II/INH the positive CD band at 274 nm disappeared and the negative band at 246 nm showed a decrease in the mean residual ellipticity value, indicating binding of Cu/sup II/INH to DNA. 31P NMR studies indicated that the binding of copper in Cu/sup II/INH is to the phosphate oxygen of the DNA backbone. The binding of Cu/sup II/INH was also found to be reversible. Addition of ethylenediaminetetraacetic acid to the Cu/sup II/INH-DNA complex resulted in breaking of the complex and restoring the original structure features of the B family of DNA in the resulting fragments. At the concentration level of Cu/sup II/INH employed, both CuSO4 and INH independently did not show any interaction with DNA