Proteinase K is a highly active 28,904-Da serine protease isolated from the fungus Tritirachium album.

The enzyme exhibits broad cleavage specificity on native and denatured proteins and is widely used in the purification of DNA and RNA. Its activity is increased in the presence of denaturants such as SDS (1%) and elevated temperature (50 to 60 °C). Working concentration is 50 to 100 µg/ml for protein removal and enzyme inactivation and upto 2 mg/ml for tissue treatment. It is a lyophilized powder.