We are requesting for a differential scanning calorimeter ( DSC) equipped with extended temperature range (220C), an external cooling unit, data collection and analysis system and software and reusable cells. This is the only DSC with the requisite sensitivity and temperature range offered. The acquisition of this instrument will permit the P.I.'s to analyze the thermal denaturation characteristics of enzymes from thermophilic and superthermophillic organisms, to study the molecular mechanism of thermal denaturation of small proteins of know structure, to analyze thermodynamic basis of action of a protease inhibitor of physiological significance and to explore the significance of subunit and domain interactions in producing activity in an enzyme. These studies will extend our knowledge of the structural basis of thermal stability in proteins and activity in enzymes.