Proteinase K is a nonspecific serine protease. It is not inactivated by metal ions, chelating agents (e.g. EDTA), sulfyhydryl reagents or by trypsin or chymotrypsin inhibitors. It is stable over a wide pH (4-12.5), with optimal activity at pH 6.5-9.5. Proteinase K activity can be stimulated by addition of denaturing agents SDS and urea. The optimum temperature for the enzyme is 65C; it is twelve times more active at 65C than at 25C. However, rapid denaturation of the enzyme will occur at temperatures above 65C. Thus, protein digestion is usually carried out at 55C. Autolysis of the enzyme occurs increasingly at alkaline pH. However, proteinase K is not completely inactivated by autolysis, and some enzyme fragments maintain proteolytic activity even after extensive autolysis