An. Veselkov et al., H-1-NMR INVESTIGATION OF THE INTERACTION OF ETHIDIUM-BROMIDE WITH TETRADEOXYRIBONUCLEOSIDE TRIPHOSPHATE 5'-D(GCGC), Molecular biology, 29(2), 1995, pp. 187-195
Complex formation between ethidium bromide and self-complementary tetr
adeoxyribonucleoside triphosphate 5'-d(GCGC) in water-salt solution wa
s studied by one-dimensional and two-dimensional 500-MHz H-NMR spectro
scopy. Concentration dependences of proton chemical shifts were measur
ed at a constant temperature of 308 degrees K. Different schemes of co
mplex formation between the dye and tetranucleotide were considered. T
he equilibrium constants of reactions were determined, as well as the
limit values of the chemical shifts of protons of ethidium bromide in
the complex. The peculiarities of the dynamic equilibrium between diff
erent types of complexes depending on relative concentrations of dye a
nd tetranucleotide were revealed. The conclusion is made that ethidium
bromide intercalates preferentially into the pyrimidine-purine fragme
nt of the tetranucleotide duplex (CG site). Ethidium bromide intercala
tes at the minor groove of the duplex, in contrast to proflavine, whic
h binds at the major groove of the double helix. The most plausible st
ructure of the 1:2 complex of the dye with tetranucleotide is suggeste
d, which agrees well with the results of X-ray investigations of Sobel
l et al.