Thermo Scientific Pierce Proteinase K is a protease that cleaves at the carboxyl side of aliphatic, aromatic or hydrophobic residues and is commonly used to digest and inactivate DNase and RNase in nucleic acid purification.

Proteinase K is a subtilisin-like endolytic protease that is isolated from the saprophytic fungus Tritirachium album. It has a high activity that is stable across a wide range of pH and temperature conditions and is suited to short digestion times. The activity of proteinase K is increased at elevated temperatures up to 65°C. Calcium is not essential to the function of proteinase K. Therefore, EDTA and other chelating agents do not interfere with the activity and may be used alongside proteinase K to inactivate calcium-dependent nucleases in DNA and RNA preparation.