THE THERMODYNAMICS OF THE UNFOLDING OF AN ISOLATED PROTEIN SUBDOMAIN - THE 255-316-C-TERMINAL FRAGMENT OF THERMOLYSIN

Differential scanning calorimetry has been used to study the thermal u nfolding of the 255-316 C-terminal fragment of thermolysin. The concen tration effect on the calorimetric transitions of the fragment in 0.1 M NaCl and 20 mM phosphate buffer, pH 7.5, shows that it behaves as a highly stable dimer in solution, whithin the concentration range 0.19- 4.55 mg/ml, undergoing a reversible two-state thermal unfolding proces s. The thermodynamic parameters of unfolding (Delta G = 60 +/- 6 kJ/(m ol of dimer) at 20 degrees C) are similar to those normally observed f or small, compact, globular proteins. This and previous studies [1989, Eur. J. Biochem. 180, 513-518] show that the 255-316 fragment folds i nto a stable, native-like globular structure.