Phosphorus-31 nuclear magnetic resonance studies of actinomycin D, ethidium bromide, and 9-aminoacridine complexes with dinucleotides
Abstract
Phosphorus-3 1 nuclear magnetic resonance spectra of actinomycin D, ethidium bromide, and 9-aminoacridine complexes with deoxydinucleotides and ribodinucleoside monophosphates are reported. In the 2:1 pdGpdCactinomycin D complex, the internucleotide phosphorus resonances exhibit individual resonances in the slow exchange region at - 18 degrees C which are - 1.7 and -2.4 ppm downfield of the resonance from the internucleotide phosphorus (atom) in a pdGpdC solution under similar expeiimental conditions. These complexation shifts result from the formation of a miniature intercalated complex. The formation of an intercalated complex of actinomycin D with the complementary mixture of deoxydinucleotides pdGpdT and pdApdC resulted in complexation shifts of -0.2 and -0.75 ppm (-16 degrees C) for the internucleotide phosphates of pdCpdT and pdApdC, respectively. The phosphorus-3 1 complexation shifts are also reported for several other actinomycin D solutions with mixtures of complementary and noncompiementary deoxydinucleotides. Ethidium bromide forms miniature intercalated complexes with pdCpdG and CpG which result in complexation shifts of -0.1 ppm and +0.2 ppm (2:l nucleotide-ethidium bromide solutions at 6 degrees C), respectively. A +O. 15 ppm complexation shift is observed in a 2.2:1 CpG-9-aminoacridine solution at 3 degrees C. These phosphorus-31 chemical shift data suggest that both the structure of the intercalating drug and the sequence of the nucleotides at the intercalation site influence the geometry of the intercalated complex, although at the present time it is not possible to quantitatively interpret these complexation shifts in terms of changes in the geometry of the sugar-phosphate backbone of the nucleic acid.