What is the relationship between proteinase K and calcium?

Proteinase K binds to two Ca 2+ ions to assist in maintaining the stability of the enzyme, especially when exposed to increasing temperatures. Additionally, calcium protects proteinase K from autolysis. It has been shown the Ca(2+) removal decreased the enzyme’s overall thermal stability and to a certain degree the substrate affinity. Calcium however is not necessary for proteolytic activity and is not directly involved in the catalytic mechanism.