Proteinase K is a non-specific serine protease having a very high specific activity. It is used to purify target material from contaminating proteins, for the isolation of mRNA or high molecular weight DNA and to inactivate other enzymatic activities. Proteinase K is active with or without the presence of SDS, EDTA and urea.

Proteinase K is stable in a wide variety of detergents and buffer salts and at various temperatures and pH. The isoelectric point of proteinase K is 8.9.

Proteinase K is typically used at a concentration of 50-100 μg/ml. It is active with or without the presence of SDS, urea, EDTA or various metal ions, but the activity of proteinase K can be increased by adding the denaturing agents and the structure of proteinase K can be stabilized by addition of Ca2+. Proteinase K is inactivated by heating to 95°C for 10 minutes or using an inhibitor such as PMSF, AEBSF or DFP.