Effect of glycerol on the interactions and solubility of bovine pancreatictrypsin inhibitor

The effects of additives used to stabilize protein structure during crystal lization on protein solution phase behavior are poorly understood. Here we investigate the effect of glycerol and ionic strength on the solubility and strength of interactions of the bovine pancreatic trypsin inhibitor. These two variables are found to have opposite effects on the intermolecular for ces; attractions increase with [NaCl], whereas repulsions increase with gly cerol concentration. These changes are mirrored in bovine pancreatic trypsi n inhibitor solubility where the typical salting out behavior for NaCl is o bserved with higher solubility found in buffers containing glycerol. The in creased repulsions induced by glycerol can be explained by a number of poss ible mechanisms, all of which require small changes in the protein or the s olvent in its immediate vicinity. Bovine pancreatic trypsin inhibitor follo ws the same general phase behavior as other globular macromolecules where a robust correlation between protein solution second virial coefficient and solubility has been developed. This study extends previous reports of this correlation to solution conditions involving nonelectrolyte additives.