INTERCALATION OF 6 BETA-CARBOLINE DERIVATIVES INTO DNA

The absorption spectra, ethidium bromide fluorescent spectra and circu lar dichroism (CD) spectra indicate that six beta-carboline derivative s, norharman, harman, harmol, harmine, harmalol and harmaline intercal ate into DNA. This result is supported by unwinding experiments using the superhelical plasmid pBR322 DNA, and the magnitude of intercalatio n except for harmalol decreased in the order of harmol>harmine>harmali ne>harman>norharman. The potency of the interactions was further deter mined by spectrophotometric titration. The Scatchard plots were then a nalyzed using the Langmuir equation including two terms for specific a nd non-specific interactions. The interaction of the beta-carboline de rivatives with DNA is characterized as follows : 1) Substitution into the beta-carboline skeleton rings decreases the number of binding site s. 2) The polar groups OH and OCH, increase the binding affinity at th e first specific term. 3) A decrease in the planarity of the beta-carb oline skeleton decreases the binding affinity. 4) The interaction of h armalol with DNA may be less potent than that of harmine.