Premium
Interaction of poly‐5‐bromouridylic acid. II. Thermodynamic analysis of its interaction with adenosine and 9‐methyladenine
Author(s) -
Higuchi Shigesada,
Yasui Kumiko
Publication year - 1984
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.360230420
Subject(s) - chemistry , isothermal microcalorimetry , monomer , adenosine , enthalpy , standard enthalpy of formation , interaction energy , thermodynamics , crystallography , stereochemistry , medicinal chemistry , organic chemistry , molecule , biochemistry , physics , polymer
The interaction of poly‐5‐bromouridylic acid [poly(BU)] with adenosine and 9‐methyladenine was studied by equilibrium dialysis, optical melting, and microcalorimetry. The stacking free energy, ω, was estimated as −17.6 kJ/mol for adenosine·2poly(BU) and −18.8 kJ/mol for 9‐methyladenine·2poly(BU) from the binding isotherms constructed from equilibrium dialysis results. The binding isotherms constructed from a series of melting curves also gave ω values for adenosine·2poly(BU). The thermal stability of the complex depends on monomer concentration, and the partial molar enthalpies of the complex formation at the midpoint of the transition were evaluated from the T m coefficients as a function of free monomer concentration. The values of −92.0 and −90.4 kJ/mol were obtained for adenosine·2poly(BU) and 9‐methyladenine·2poly(BU) in 0.4 M NaCl–0.02 M Na‐cacodylate–5 × 10 −4 M EDTA (pH 7.0), respectively. Microcalorimetric measurements provided lower integral heats of reaction values for these complexes, i.e., −73.2 kJ/mol for adenosine·2poly(BU) and −71.5 kJ/mol for 9‐methyladenine·2poly(BU). A comparison with a polyribouridylic acid system provided a quantitative understanding of a stabilization by bromination in terms of thermodynamic parameters.