Albany 2001

category image Biomolecular
SUNY at Albany
June 19-23, 2001

pH-Induced Helix-Coil Transition of EtBr Ð DNA Complexes

Helix-coil transition of DNA Ð Ethidium Bromide (EtBr) complexes has been investigated using variation of pH as a melting factor at low range of pH. It has been shown that EtBr stabilized the helix structure of DNA preferentially interacting with AT base pairs of the biopolimer. This resulted in decreased transition-width of the complexes (DpH) with respect to that of "pure" DNA (D0pH) at low EtBr concentrations (c=EtBr/DNA b.p. £0.02) .Upon further increase in ligand concentration (0.02{}£0.2) DpH increased and at cÅ0.2 became equal to D0pH .The point of transition (DpHm) decreased monotonically at the all range of variation of c.

We examined the binding isotherms of EtBr to ds- and ss-DNA over a wide concentration range including ligand concentration at which saturation of the biopolymer with dye occurred. In our investigation we applied absorption and fluorescence spectroscopy methods. The data revealed two "strong" interactions of EtBr with ds-DNA one of which corresponded to intercalation ("fluorescent" type) and the other nonfluorescent type. Nonlinear Scatchard plotes for the complexes of ss-DNA-EtBr were obtained which at pHÅ3, t=25 0C and µ=20mM Na+ has been analysed in term of two independent types of interactions. The binding constants Ki and binding site size ni have been calculated at pHÅ3. The derived data are in very good agreement with the similar data obtained at pHÅ7 and t=70 0C.

Ara P. Antonyan, Pogos O. Vardevanyan and Armen T. Karapetian(1)*.

Biophysics Department of Yerevan State University, Yerevan 375025, Armenia.
*Physics Department of Yerevan Institute of Architecture and Construction(1), Yerevan 375009, Armenia.
* Phone: (3741)580 691; E.mail: karam@edu.am