Studies on the interaction of cupric isonicotinohydrazide with DNA

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Abstract
The interaction of cupric isonicotinohydrazide (CuIIINH), an antiviral compound, with calf thymus DNA was investigated by circular dichroism (CD) and nuclear magnetic resonance (NMR). Gel electrophoresis of DNA incubated with CuIIINH showed cleavage of DNA to various extents. This cleavage was found to be time and concentration dependent. In the presence of CuIIINH 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 CuIIINH to DNA. 31P NMR studies indicate that the binding of copper in CuIIINH is to the phosphate oxygen of the DNA backbone. The binding of CuIIINH was also found to be reversible. Addition of ethylenediaminetetraacetic acid to the CuIIINH-DNA complex resulted in breaking of the complex and restoring the original structural features of the B family of DNA in the resulting fragments. At the concentration of CuIIINH employed, both CuSO4 and INH independently did not show any interaction with DNA.