28,900 daltons. pH Optimum: 7.5 - 12, using denatured hemoglobin as substrate. Stability: 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)

≥400 units per milliliter