Chelerythrine, a new benzo[c]phenanthridine based converter of alternate DNA structure into conventional one: A spectroscopic exploration

Association of different polymprphic forms of DNA having alternating G-C sequences with the alkaloid Cheler-ythrine Chloride (CHL) was probed by using UV absorption and circular dichroism (CD) spectrometry. Spec-trophotometric titration revealed that the association of CHL with right handed B-form was non-cooperative in nature with higher binding affinity (-106 M-1) in contrast to the cooperative binding with left handed Z-form and HL-form where the intrinsic binding constants were of the order of-104 M-1. Further, conversion of the left-handed Z-form and the HL-form of the polymer back to the bound right-handed form by CHL has been evidenced from CD spectroscopy and under our experimental condition, the number of base pairs of Z-form and HL-form that switched to right-handed conformation by each bound CHL molecule was found to be 2-3. Moreover, kinetic measurements showed that in presence of increasing concentration of CHL, both the rate and the extent of B-form to Z-form transition were reduced.