This enzyme is closely associated with an endotoxin-sensitive hemolymph coagulation system which may play important roles in both hemostasis and host defense mechanisms (PubMed:3512266). Its active form catalyzes the activation of clotting factor B (PubMed:3512266). Selective cleavage of 103-Arg-|-Ser-104 and 124-Ile-|-Ile-125 bonds in Limulus clotting factor B to form activated factor B. Cleavage of -Pro-Arg-|-Xaa- bonds in synthetic substrates. Activated by Gram-negative bacterial lipopolysaccharides (PubMed:3512266). Inhibited by intracellular coagulation inhibitor 1/LICI-1 and to a lesser extent by intracellular coagulation inhibitors 2/LICI-2 and 3/LICI-3 (PubMed:8276848, PubMed:7822280, PubMed:8798603). Inhibited by the small molecule diisopropyl fluorophosphate (DFP) (PubMed:3512266). Heterodimer of a light chain and a heavy chain linked by a disulfide bond (PubMed:3308457, PubMed:3512266). Forms a covalent heterodimer with intracellular coagulation inhibitor 1/LICI-1 (PubMed:8276848). Forms a covalent heterodimer with intracellular coagulation inhibitor 2/LICI-2 (PubMed:7822280). Secreted in hemolymph (PubMed:2007602). Localizes in large granules of hemocytes (PubMed:2007602). Expressed in hemocytes (at protein level). N-glycosylated. Lipopolysaccharide (LPS) activates clotting factor C by inducing the proteolytic cleavage of the clotting factor C light chain into clotting factor C chains A and B (PubMed:3308457, PubMed:3512266). Clotting factor C chains heavy, A and B remain associated via interchain disulfide bonds (PubMed:3512266). Belongs to the peptidase S1 family.