Serine protease which, by cleaving and activating prophenoloxidase (PPO1) after immune challenge, plays an essential role in the melanization immune response to wounding. Inhibited by aprotenin. Not inhibited by EDTA, PMSF or leupeptin. Secreted in the hemolymph. Expressed in hemocytes. Expressed in larvae. Upon physical injury. Up-regulated 5-fold after 6 hours and 15-fold after 18 hours of injury. The clip domain consists of 35-55 residues which are 'knitted' together usually by 3 conserved disulfide bonds forming a clip-like compact structure. Activated by the removal of the N-terminal inhibitory propeptide. Belongs to the peptidase S1 family. CLIP subfamily.