THERMODYNAMICS OF HELIX-COIL TRANSITION OF ALTERNATING COPOLYMER OF DEOXYADENYLIC ACID AND DEOXYTHYMIDYLIC ACID

The method of differential heat capacity calorimetry (Danforth, Krakauer & Sturtevant, 1967) is applied to the study of the helix-coil transition of the alternating copolymer of deoxyadenylic acid and deoxythymidylic acid, poly (dAT).‡ ‡ The melting behavior as observed calorimetrically is similar to that observed spectrophotometrically. The apparent enthalpy and heat capacity of the coil form at 40 °C are respectively 7.90 ± 0.14 kcal, (mole of base pairs)-1 and 20 ± 16 cal. deg.-1 (mole of base pairs)-1 higher than those of the helical form. The enthalpy change is close to that previously reported (Krakauer & Sturtevant, 1968) for poly (A + U). © 1969.