Molecular aspects on the interaction of sanguinarine with B-form, Z-form and H-L form DNA structures

The interaction of sanguinarine with right-handed (B-form), left-handed (Z- form) and left-handed (H-L-form) structures of. poly(dG-dC).poly(dG-dC) has been investigated by measuring the circular dichroism (CD) and UV-absorpti on spectral analysts. Sanguinarine binds strongly to the B-form DNA and doe s not bind to Z-form or H-L-form, but it converts the Z-form and the H-L-fo rm back to the bound right handed form as evidenced from CD spectroscopy. S anguinarine inhibits the rate of B to Z transition under ionic conditions t hat otherwise favour the left-handed conformation of the polynucleotides. U V absorption kinetic studies show that the Z-form reverses back to B-form o n binding to sanguinarine. Binding isotherms obtained from spectrophotometr ic data show that sanguinarine binds strongly to the B-form polymer in a no n-cooperative manner, in sharp contrast to the highly cooperative interacti on under Z-form and H-L-form polynucleotides. These studies reveal that the alternating GC sequence undergoes defined conformational changes and inter acts with sanguinarine which may be no important aspect in understanding it s extensive biological activities.