Proteases can destroy your sample prep in a hurry unless you include the appropriate mix or cocktail of protease inhibitors. A protease inhibitor cocktail can protect the integrity of your sample prep for protein purification, DNA prep, chromatin immunoprecipitation, bacterial lysates, crude tissue extracts, and more. Some cocktails include EDTA for metalloprotease inhibition, but it is not appropriate for every sample. The use of EDTA and each protease component in the cocktail should be matched with your sample to make sure that it is compatible with your research goal.