Abstract
Proteins are fragile molecules that often require great care during purification to ensure that they remain intact and fully active. Removal of proteins from the cellular environment subjects them to a variety of conditions and processes that can lead to loss of activity or alteration of structure. If the protein of interest is lost or inactivated during the course of any procedure, the determination of the reason for this loss can often suggest a simple solution. Thus, if possible, it should be examined whether the loss of activity is accompanied by loss of the protein or changes in its structure or whether the protein remains but is now inactive. Protein solutions should not be exposed to extremes of pH, high temperatures, organic solvents, or any other condition that might promote denaturation. Likewise, if a protein solution is stored for extended periods in an unfrozen state, bacterial and fungal growth can become a problem.