<P> Currently more than 50 clans are known, each indicating an independent evolutionary origin of proteolysis . </P> <P> Alternatively, proteases may be classified by the optimal pH in which they are active: </P> <Ul> <Li> Acid proteases </Li> <Li> Neutral proteases involved in type 1 hypersensitivity . Here, it is released by mast cells and causes activation of complement and kinins . This group includes the calpains . </Li> <Li> Basic proteases (or alkaline proteases) </Li> </Ul> <Li> Neutral proteases involved in type 1 hypersensitivity . Here, it is released by mast cells and causes activation of complement and kinins . This group includes the calpains . </Li>

Where is proteases found in the human body