Studies on Limulus amoebocyte lysate. III. Purification of an endotoxin-binding protein from Limulus amoebocyte membranes.

A protein that has been isolated from Limulus polyphemus amoebocyte membranes binds endotoxin. The protein was purified by two independent methods, organic solvent extraction and affinity chromatography, both followed by gel filtration. Immunologic studies confirm that the protein is a component of amoebocyte membranes. Although without enzymatic activity, the binding protein enhances Limulus lysate gelation. As a membrane-associated endotoxin binding "protein," it may be involved in Limulus lysate coagulation, which is initiated by minute amounts of Gram-negative bacterial endotoxin. The protein has an apparent molecular weight of 80,000.