This enzyme is closely associated with an endotoxin-sensitive hemolymph coagulation system which may play important roles in both hemostasis and host defense mechanisms. Its active form catalyzes the activation of proclotting enzyme. Does not activate the mammalian coagulation factors factor IX, factor X, prothrombin, plasminogen, protein C or prekallikrein. Does not hydrolyze fibrinogen. Does not catalyze the activation of factor C or coagulogen. Selective cleavage of 98-Arg-|-Ile-99 bond in Limulus proclotting enzyme to form active clotting enzyme. Strongly inhibited by alpha2-plasmin inhibitor and DFP. Partially inhibited by benzamidine, leupeptin and PCMB. Upon activation by factor C, it is converted to a two-chain active form composed of a light and a heavy chain linked by a disulfide bond. Secreted in hemolymph. The clip domain consists of 35-55 residues which are 'knitted' together usually by 3 conserved disulfide bonds forming a clip-like compact structure. Belongs to the peptidase S1 family. CLIP subfamily.