Stabilization of lyophilized porcine pancreatic elastase

Porcine pancreatic elastase, a well-characterized serine protease, has been used as a model to assess the effects of excessive humidity on solid-state stability of the lyophilized protein. Elastase lyophilized without excipients retained full activity immediately after freeze-drying but became denatured upon continued storage at 40 degrees C, 75% relative humidity. The extent of inactivation could be monitored through assays of amidolytic activity, as well as through changes in the circular dichroism (CD) and fluorescence spectra. Differential scanning calorimetry (DSC) was employed as a means of screening potential stabilizing additives; based on the results, sucrose and dextran 40 were selected for further evaluation. Both additives were effective in preventing denaturation. Possible mechanisms for the denaturation and stabilization of elastase are discussed.