# Cooperative Nonenzymic Base Recognition - A Study of Interaction of Oligoguanylic Acid with Poly C

Podder, SK (1972) Cooperative Nonenzymic Base Recognition - A Study of Interaction of Oligoguanylic Acid with Poly C. In: Biopolymers, 11 (7). pp. 1395-1410.

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## Abstract

The interaction between poly C and (Gp)nG(n = 1,2) in dilute solution was investigated spectrophotometrically in 0.1M phosphate buffer pH 7.2 under conditions unfavorable for the formation of self-associated complexes of oligoguanylic acids. Two isosbestic points were observed when poly C was titrated gradually with GpGpG, one at 232-233 m\mu(in the range of 0-33% poly C) and one around 238 m\mu (in the range of 50-100% poly C). The melting temperature ($T_m$) of the 1:1 poly C: (Gp)nG complexes (n = 1,2) of varying concentration were determined. The equilibrium properties of the 1:1 complexes can be described by two interaction parameters, namely, (i) cooperative stacking interaction between the first nearest neighbor of the adsorbed oligomer, and (ii) intrinsic association constant of the adsorbed oligomer with its polymeric site, since the cooperative helix-coil transition particularly in the smaller oligonucleotide can be described by an "all or none" model. Based on such a model the enthalpy of stacking inteaction-dependent $T_m$ values yielded directly the sum of the enthalpy of stacking interaction and of basepairing (which is dependent on the chain length of the oligomer) and the value of S, the stability constant of a G-C pair within a helix. The enthalpy of formation of G-C pair is then calculated as -6.3 kcal/base pair either from the chain length dependent enthalpy term or from the temperature coefficient of S values. From the S value and the association constant of 1:1 GpGpGpC:GpCpCpC complex, other thermodynamic parameters such as nucleation parameter (\beta) and free energy of stacking interaction can be obtained.

Item Type: Journal Article Biopolymers John Wiley & Sons, Inc. The copyright belongs to John Wiley & Sons, Inc. Division of Biological Sciences > Biochemistry 09 Feb 2007 19 Sep 2010 04:21 http://eprints.iisc.ac.in/id/eprint/4052