Proteinase K from the fungus Engyodontium album is a nonspecific serine protease that is useful for general digestion of proteins. Proteinase K remains active:

• Over a wide pH range—optimal activity between 6.5 and 9.5
• Under denaturing conditions—e.g., in the presence of SDS or urea
• In the presence of metal chelating agents—e.g., EDTA
• At comparatively high temperatures—optimum digestion temperature is 65°C

Applications
Removal of endogenous nucleases during the preparation of DNA and RNA; preparation of tissue sections for in situ hybridization.

Performance and quality testing
Endodeoxyribonuclease and exodeoxyribonuclease assays; liquid form tested for absence of RNase activity.

Unit definition
One mAnson unit is described as that amount of enzyme that liberates 1 μmole of Folin-positive amino acid within 1 min at 37°C using hemoglobin as a substrate.