:Limulus clotting enzyme

{{Infobox enzyme

| Name = Limulus clotting enzyme

| EC_number = 3.4.21.86

| CAS_number =

| GO_code =

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Limulus clotting enzyme ({{EC number|3.4.21.86}}, clotting enzyme) is an enzyme.{{cite journal | vauthors = Muta T, Hashimoto R, Miyata T, Nishimura H, Toh Y, Iwanaga S | title = Proclotting enzyme from horseshoe crab hemocytes. cDNA cloning, disulfide locations, and subcellular localization | journal = The Journal of Biological Chemistry | volume = 265 | issue = 36 | pages = 22426–33 | date = December 1990 | doi = 10.1016/S0021-9258(18)45722-5 | pmid = 2266134 | doi-access = free }}{{cite journal | vauthors = Tokunaga F, Nakajima H, Iwanaga S | title = Further studies on lipopolysaccharide-sensitive serine protease zymogen (factor C): its isolation from Limulus polyphemus hemocytes and identification as an intracellular zymogen activated by alpha-chymotrypsin, not by trypsin | journal = Journal of Biochemistry | volume = 109 | issue = 1 | pages = 150–7 | date = January 1991 | doi = 10.1093/oxfordjournals.jbchem.a123337 | pmid = 2016264 }} This enzyme catalyses the following chemical reaction:

: Selective cleavage of -Arg¹⁸- and -Arg⁴⁷- bonds in coagulogen to form coagulin and fragments

This enzyme is present in the hemocyte granules of horseshoe crabs Limulus and Tachypleus. In the immunity-related clotting pathways of these organisms, it is the final enzyme responsible for the activation of coagulin.{{cite journal |last1=Iwanaga |first1=S |title=Biochemical principle of Limulus test for detecting bacterial endotoxins. |journal=Proceedings of the Japan Academy. Series B, Physical and Biological Sciences |date=May 2007 |volume=83 |issue=4 |pages=110–9 |doi=10.2183/pjab.83.110 |pmid=24019589 |pmc=3756735|bibcode=2007PJAB...83..110I }}