VOLUME CHANGES ACCOMPANYING THERMAL DENATURATION OF DEOXYRIBONUCLEIC ACID .I. DENATURATION AT NEUTRAL PH

Dilatometric measurements were made to determine the change in apparent specific volume φ of DNA resulting from thermal denaturation in neutral solution, φ increased continuously with temperature in the range 10–85°C. No deviations from a monotonically rising curve were observed in the φ versus temperature profile in the region of the melting temperature. The results are interpreted in terms of a partial loss of the preferentially bound DNA hydration shell. The nature of the well known buoyant density difference between native and denatured DNA was investigated by evaluating the densities in a series of cesium salt gradients at constant temperature. Extrapolation of the results to zero water activity indicates that the partial specific volumes of anhydrous native and denatured DNA are equal. The density difference at nonzero water activities is attributed to decreased hydration in the denatured state. The absence of a related change in φ accompanying the denaturation in the dilatometric experiments suggests that the probable volume change associated with loss of bound water during denaturation is accompanied by other compensatory volume effects. The possible nature of these volume effects is discussed. Copyright © 1969 John Wiley & Sons, Inc.