Proteinase K

Proteinase K (also protease K or endopeptidase K) is a broad-spectrum serine protease. The enzyme was discovered in 1974 in extracts of the fungus Tritirachium album.

Proteinase K is commonly used in molecular biology to digest protein and remove contamination from preparations of nucleic acid. Addition of proteinase K to nucleic acid preparations rapidly inactivates nucleases that might otherwise degrade the DNA or RNA during purification. It is highly-suited to this application since the enzyme is active in the presence of chemicals that denature proteins, such as SDS and urea, chelating agents such as EDTA, sulfhydryl reagents, as well as trypsin or chymotrypsin inhibitors. Proteinase K is also stable over a wide pH range (4-12), with a pH optimum of pH 7.5-12.

The enzyme's activity towards native proteins is stimulated by denaturants such as SDS, but when measured using peptide substrates, the reverse is seen, with these chemicals inhibiting the enzyme. The reason for this result is that the denaturing agents unfold the protein substrates and make them more accessible to the protease.