Limulus clotting enzyme (EC 3.4.21.86, clotting enzyme) is an enzyme. This enzyme catalyses the following chemical reaction Limulus clotting enzyme (EC 3.4.21.86, clotting enzyme) is an enzyme. This enzyme catalyses the following chemical reaction This enzyme is present in the hemocyte granules of horseshoe crabs Limulus and Tachypleus.