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Pressure dependence of the helix–coil transition temperature of poly[d(G‐C)]
Author(s) -
Wu John Q.,
Macgregor Robert B.
Publication year - 1995
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.360350404
Subject(s) - chemistry , helix (gastropod) , electromagnetic coil , transition (genetics) , thermodynamics , crystallography , biochemistry , physics , ecology , snail , gene , electrical engineering , biology , engineering
The Pressure Dependence of the Helix‐Coil Transition Temperature ( T m ) of Poly[d(G‐C)] was studied as a function of sodium ion concentration in phosphate buffer. The molar volume change of the transition (Δ V ) was calculated using the Clapeyron equation and calorimetrically determined enthalpies. The Δ V of the transition increased from +4.80 (±0.56) to +6.03 (±0.76) mL mol −1 as the sodium ion concentration changed from 0.052 to 1.0 M . The van't Hoff enthalpy of the transition calculated from the half‐width of the differentiated transition displayed negligible pressure dependence: however, the value of this parameter decreased with increasing sodium ion concentration, indicating a decrease in the size of the cooperative unit. The volume change of the transition exhibits the largest magnitude of any double‐stranded DNA polymer measured using this technique. For poly[d(G‐C)] the magnitude of the change in Δ V with sodium ion concentration (0.94 ± 0.05 mL mol −1 ) is approximately one‐half that observed for either poly[d(A‐T)] or poly (dA)·poly(dT). The Δ V values are interpreted as arising from changes in the hydration of the polymer due to the release of counterions and changes in the stacking of the bases of the coil form. As a consequence of solvent electrostriction, the release of counterions makes a net negative contribution to the total Δ V , implying that disruption of the slacking interactions contributes a positive volume change to the total Δ V . The larger magnitude of the Δ V compared with that of other double‐stranded polymers may be due in part to the high helix‐coil transition temperature of poly[d(G‐C)], which will attenuate the contribution of electrostriction to the total volume change. The data in addition show that in the absence of other cellular components, the covalent structure of DNA is stabile under conditions of temperature and pressure more extreme than those experienced by any known organism. © 1995 John Wiley & Sons, Inc.