Protein heat capacity reflects the dynamics of enthalpy exchange between the single macromolecule and the surroundings

Heat capacity has played a prominent role in relating macroscopic and micro scopic properties of small molecules and crystals. However, its diagnostic power can also be used for macromolecules such as proteins. It is shown in the present study that the macroscopically observed protein heat capacity p rovides direct access to the thermodynamic state of the single protein mole cule. The new model of the physical basis of protein heat capacity emphasiz es the dynamic nature of protein molecules, It incorporates equilibrium flu ctuations as an integral constituent and shows that the increase in the mag nitude of equilibrium fluctuations is coupled to an increase in the enthalp y flux between the individual protein molecule and its surroundings. (C) 20 00 Wiley-Liss, Inc.