Cysteine protease which may be involved in digestion. Shows highest affinity for proline at the P2 position. Cleaves valine more efficiently than leucine and exhibits 10-fold lower affinity for phenylalanine than proline. Can cleave type I collagen. Optimum pH is 6.0. Unstable at pH values less than 5.0 and remains fully active over a wide alkaline pH range. Optimum temperature is 40 degrees Celsius but displays considerable activity as low as 20 degrees Celsius. Thermostable. Retains 60% of initial activity after incubation at 50 degrees Celsius for 2 hours. Belongs to the peptidase C1 family.