900 daltons (~28.9 KDa). Although calcium ions do not affect the enzyme activity
they do contribute to its stability when present at a concentration of 1 - 5 μmoles. An interesting characteristic of proteinase K is that it retains its activity in the presence of sodium dodecyl sulphate (SDS) or urea. (0.5 - 1% SDS and 1 - 4 M urea). Raising the temperature of the reaction from 37°C to 50°C - 60°C can increase the activity several folds. A special feature of proteinase K is its ability to digest native proteins