Albany 2019: 20th Conversation - Abstracts

category image Albany 2019
Conversation 20
June 11-15 2019
Adenine Press (2019)

Binding peculiarities of ethidium bromide to polyguanine acid

Ethidium bromide (EtBr) binding to poly(G)4 has been studied using spectroscopic methods at the solution ionic strengths 0.11, 0.31 and 0.51 M. Spectral characteristics (changes of absorption and fluorescence spectra) of EtBr-poly(G)4 complexes are analogous to those obtained for EtBr complexes with DNA or poly(rA)-poly(rU) (Bochman et al, 2012). The studies were carried out at the temperatures 293 K, 298 K and 300 K to determine the binding thermodynamic parameters. Based on the absorption and fluorescence spectra the binding curves in Scatchard’s coordinates were constructed at the mentioned ionic strengths of the solution and temperatures (EtBr binding curves to poly(G)4 in Scatchard’s coordinates are similar to those obtained for this ligand complexes with DNA), and the values of binding constant K and binding site size n, ΔG, ΔH and ΔS were determined by standard formulas.

Value of the enthalpy change (ΔH ~ -2.2 ccal/mol) is about three-fold less, than in the case of intercalation binding of EtBr to double-stranded NA and the binding constant value K is about an order less, than the analogous value corresponding to EtBr intercalation into the plane of ds-NA base pairs. Most probably, it is the fact that at the mentioned conditions EtBr binds to poly(G)4 by semi-intercalation mode. It is indicated by the fact that the values of ΔG and ΔS are in correspondence to those obtained for EtBr complexes with single- or double-stranded DNA at the binding semi-intercalation mode.

The obtained data indicate that EtBr binding modes to nucleic acids depend on structural state of the latters. Particularly, in the case of NA structure dense packaging, EtBr intercalation becomes difficult and the main binding mode remains semi-intercalation, as it was revealed for this ligand complexes with poly(G)4. Consequently, by investigating interactions of synthetic four-stranded polyguanylic acid with EtBr, we can understand the structural differences of studied synthetic and right-handed B- or A-conformational types of nucleic acids, at the same external conditions.


Bochman, M.L., Paeschke, K., Zakian, V.A. (2012). DNA secondary structures: stability and function of G-quadruplex structures. Nat. Rev. Genet. 13, 770-780.

Marine A.Parsadanyan1*
Ara P.Antonyan1
Mikayel V.Minasyants2
Armen T.Karapetian3

1Department of Biophysics
Yerevan State University
Yerevan, Armenia
2 UWC Dilijan College
Dilijan, Armenia
3 Department of Physics and Electrotechnics
Natioanl University of Architecture and Construction of Armenia
Yerevan, Armenia

Ph: (+37460) 710522
Email: marine.parsadanyan@ysu.am