Premium
Calorimetric investigation of the helix–coil conversion of polyuridylic acid
Author(s) -
Heinecke Marion,
Bode Diedrich,
Schernau Ulrich
Publication year - 1974
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.1974.360130116
Subject(s) - chemistry , cooperativity , enthalpy , helix (gastropod) , isothermal process , calorimeter (particle physics) , base (topology) , thermodynamics , absorbance , analytical chemistry (journal) , crystallography , chromatography , ecology , mathematical analysis , biochemistry , physics , mathematics , detector , biology , snail , electrical engineering , engineering
Abstract The heats of the conformational conversion Δ H c of polyuridylic acid (polyU) in the presence of various cations were determined using a differential scanning microcalorimeter and an isothermal mixing calorimeter. The first method yields a value of Δ H c = 5.2 kcal/mol of base pairs, the second one a value of Δ H c = 6.4 kcal/mol of base pairs. Knowing Δ H c and the maximal slope of the degree of conversion, which was determined from the temperature dependence of the absorbance of polyU solutions at 260 nm, we were able to evaluate the parameter of cooperativity σ. From the relation σ = e Δ F stack / RTthe stacking free energy Δ F stack could be calculated. Dividing the apparent enthalpy of conversion by the calorimetrically measured enthalpy yields the cooperative length N 0 of one helical segment at the midpoint of conversion. The results show that the type of the cation has no influence on the magnitude of Δ H c , whereas the cooperativity of polyU is influenced by the various cations.