CLOTTING PROCESSES IN CRUSTACEA DECAPODA

Summary 1. In Limulidae, all the factors involved in the coagulation processes are located inside the amoebocytes. The cellular coagulogen is a single 20,000‐polypeptide‐chain protein. It is converted into a non‐covalently crosslinked gel by a serine protease enzyme which cleaves a single peptide bond, releasing peptice C. 2. Pro‐clotting enzyme can be activated by two independent pathways: coagulation is induced by either LPS or 1,3‐β‐D‐glucan, both of which result in gel formation. The two pathways comprise a complex enzyme cascade with several limited protein proteolyses. 3. In Decapoda, clotting factors are found in both the cell‐free plasma and haemocyte compartments. Analogous factors are present in Insecta. 4. Plasma coagulogen is a 400,000 molecular weight protein with both lipid and carbohydrate moieties. Its soluble polymers are converted into covalently crosslinked polymers of coagulin by Ca 2+ ‐dependent transglutaminase. In crayfish, it is also found in other tissues such as soft integument and calcified cuticle. Its concentration varies greatly with the species investigated. It seems to possess many diversified functions such as plasma coagulation, protein transport of tanning agents, lipid and sugar transport and protein storage, and resembles fibronectin. 5. A type of cellular coagulogen seems to be present in the haemocytes of Decapoda. It can be converted to a gel by a serine protease pro‐clotting enzyme. This pro‐enzyme can be activated by either LPS or 1,3‐β‐D‐glucans. The mechanism of LPS action is not entirely clear. 1,3‐β‐D‐glucans also activate the prophenoloxidase system and cause phenoloxidase attachment to foreign surfaces of haemocyte lysates. The latter system is restricted to semi‐granular and granular haemocytes, and plays an important part in host‐defence reactions. 6. The evolutin of clotting processes throughout the phylogenetic tree is discussed.