Limulus anti-LPS factor: An anticoagulant which inhibits the endotoxin-mediated activation of Limulus coagulation system

Exposure of $\text{Limulus}$ amebocytes to bacterial endotoxins (lipopolysaccharides, LPS) results in the activation of the coagulation system, which consists of several protein components. During the separation of these components, a potent anticoagulant, named tentatively anti-LPS factor, which inhibits the endotoxin-mediated coagulation reaction, was found in both amebocytes from the hemolymphs of $\text{Tachypleus}\text{tridentatus}$ and $\text{Limulus}\text{polyphemus}$. The principle purified partially from $\text{Tachypleus}$ amebocyte lysate had a molecular weight less than 10,000, as judged with the ordinary gelfiltration experiment. It inhibited specifically the activation of factor B, which has recently been characterized to be a coagulation factor highly sensitive to LPS, but it did not inhibit the activities of the active factor B and the active clotting enzyme separated from the lysate. The inhibitory activity of anti-LPS factor disappeared almost completely by the treatments with pronase-P and subtilisin, suggesting its polypeptide-like substance, but it resisted to a boiling treatment. A possible site of the anticoagulant action on the $\text{Limulus}$ coagulation system was discussed.