Calorimetric investigation of the helix–coil conversion of polyuridylic acid

✍ Scribed by Marion Heinecke; Diedrich Bode; Ulrich Schernau

• Book ID: 101715303
• Publisher: Wiley (John Wiley & Sons)
• Year: 1974
• Tongue: English
• Weight: 470 KB
• Volume: 13
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1974.360130116

✦ Synopsis

The heats of the conformational conversion AH, 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 AH, = Fi.2 kcal/mol of base pairs, the second one a value of AH, = 6.4 kcal/mol of base pairs. Knowing AH, 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 u. From the relation u = e A F a w k / R T the stacking free energy AFstack could be calculated. Dividing the apparent enthalpy of conversion by the calorimetrically measured enthalpy yields the cooperative length N o 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 AH,, whereas the cooperativity of polyU is influenced by the various cations.