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Cooperative nonenzymic base recognition. Thermodynamics of the helix—coil transition of a monomer—polymer double helix
Author(s) -
Hoffman Geoffrey W.,
Pörschke Dietmar
Publication year - 1973
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1973.360120713
Subject(s) - chemistry , circular dichroism , helix (gastropod) , ionic strength , crystallography , monomer , stacking , nucleation , enthalpy , polymer , ionic bonding , thermodynamics , organic chemistry , ion , aqueous solution , snail , ecology , physics , biology
The double‐helical complex formed from m 6 m 9 A and poly U has been characterized by circular dichroism and u.v. spectrophotometry. The circular dichroism of the complex is similar to that of the double‐helical poly A poly U complex both in shape and in magnitude and thus indicates a quite similar structure. The double Helix–coil transition has been studied at various nucleotide concentrations and at three different ionic strengths. As expected for the binding of a base to a polymer, the Helix–coil transition is shifted to higher temperatures by increasing nucleotide concentrations, but is not affected by changes of the ionic strength. The melting curves are analyzed according to a linear Ising model taking the stacking of the monomers into account. At 0°C the equilibrium constant for nucleation is found to be 2–5 M −1 and that for chain growth is 500 M −1 . The enthalpy change associated with chain growth is −11.2 ± 1 kcal M −1 .