Structural conversion of left handed protonated form of calf thymus DNA to right handed B-DNA by the alkaloid chelerythrine

A study on the interaction of benzophenanthridine plant alkaloid chelerythrine (CHL) with low pH induced protonated form and conventional B-form DNA was carried out by using a combination of various spectroscopic and viscometric techniques. The interaction of the alkaloid with protonated form of DNA was characterized by the typical hypochromic and bathochromic shifts in the absorption spectrum, increase of thermal melting temperature, increase in solution viscosity, perturbation in circular dichroic spectrum. Binding constant for the association of CHL with protonated DNA was of the order of 105 M−1. The mode of binding of CHL with protonated DNA was characterized from the absorption spectral studies, viscosity measurements and quenching experiments. The stabilization of protonated DNA upon binding with CHL was revealed from thermal melting studies. CD spectral studies revealed that CHL converted the protonated form of CT-DNA to the right handed B-form.