Intercalation of Six β-Carboline Derivatives into DNA

The absorption spectra, ethidium bromide fluorescent spectra and circular dichroism (CD) spectra indicate that six β-carboline derivatives, norharman, harman, harmol, harmine, harmalol and harmaline intercalate into DNA. This result is supported by unwinding experiments using the superhelical plasmid pBR322 DNA, and the magnitude of intercalation except for harmalol decreased in the order of harmol>harmine>harmaline>harman>norharman. The potency of the interactions was further determined by spectrophotometric titration. The Scatchard plots were then analyzed using the Langmuir equation including two terms for specific and non-specific interactions. The interaction of the β-carboline derivatives with DNA is characterized as follows : 1) Substitution into the β-carboline skeleton rings decreases the number of binding sites. 2) The polar groups OH and OCH3 increase the binding affinity at the first specific term. 3) A decrease in the planarity of the β-carboline skeleton decreases the binding affinity. 4) The interaction of harmalol with DNA may be less potent than that of harmine.