The reversible heat denaturation of chymotrypsinogen.

Within a restricted range of pH and protein concentration crystalline chymotrypsinogen undergoes thermal denaturation which is wholly reversed upon cooling. At a given temperature an equilibrium exists between native and reversibly denatured protein. Within the pH range 2 to 3 the amount of denatured protein is a function of the third power of the hydrogen ion activity. The presence of small amounts of electrolyte causes aggregation of the reversibly denatured protein. A specific anion effect has been observed at pH 2 but not at pH 3. Both the reversible denaturation reaction and the reversal reaction have been found to be first order reactions with respect to protein and the kinetic and thermodynamic constants for both reactions have been approximated at pH 2 and at pH 3. Renatured chymotrypsinogen has been found to be identical with native chymotrypsinogen with respect to crystallizability, solubility, activation to delta-chymotrypsin, sedimentation rate, and behavior upon being heated. Irreversible denaturation of chymotrypsinogen has been found to depend on pH, temperature, protein concentration, and time of heating. Irreversible denaturation results in an aggregation of the denatured protein.