EFFECTS OF PRESSURE ON THE HELIX COIL TRANSITION OF CALF THYMUS DNA

Autor(en): NORDMEIER, E
Stichwörter: AQUEOUS-SOLUTION; Chemistry; Chemistry, Physical; CONDENSATION; COUNTERIONS; CYLINDRICAL POLY-ELECTROLYTE; LIMITING LAWS; SCATTERING; TEMPERATURE
Erscheinungsdatum: 1992
Herausgeber: AMER CHEMICAL SOC
Journal: JOURNAL OF PHYSICAL CHEMISTRY
Volumen: 96
Ausgabe: 3
Startseite: 1494
Seitenende: 1501
Zusammenfassung: 
The influences of ionic strength, I, and high pressure, P, on the helix-coil transition temperature, T(m), of calf thymus DNA have been studied by quasielastic light scattering. In the range of P = 1-4000 bar and I from 0.005 to 0.5 M using KCl as the salt it is found that T(m) increases with both I and P. The enthalpic and entropic changes for the helix-coil transition, DELTA-H and DELTA-S, are calculated by Manning's counterion-condensation theory. Both DELTA-H and DELTA-S increase with I and decrease with P, which is in good agreement with the results obtained by other authors. Additionally, the enthalpic and entropic changes, DELTA-H(VH) and DELTA-S(VH), derived by van't Hoff's equation are determined. The ratio N = DELTA-H(VH)/DELTA-H denotes the number of DNA units that melts cooperatively. Interestingly, N increases with both I and P, where simultaneously the melting width of the transition, DELTA-T(m), decreases. This may indicate that a cooperative process is more sensitive for changes in I and P than a noncooperative process. The molar volume change per DNA base pair, DELTA-V, is derived by the Clausius-Clapeyron equation and compared with the predictions of the extended counterion-condensation theory. A quite good agreement between theory and experiment is possible if special attention is dedicated to the change of the structure of water in the neighborhood of the DNA skeleton induced by the binding of counterions. Finally, it is found that pressure has no significant influence on the effective charge of the DNA, Z(eff), and its corresponding radius R(eff), Z(eff) increases only slightly with P, while R(eff), the average radius for pairwise electrostatic segment interactions, is independent of P. However, for the determination of R(eff) the Poisson-Boltzmann equation is used. Other models may yield other results, and thus further development of the helix-coil theory for polynucleotides is needed.
ISSN: 00223654
DOI: 10.1021/j100182a086

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