The LAL test is based on the fact that Gram-negative bacterial endotoxin catalyses the activation of a proenzyme. The initial rate of activation is determined by the concentration of endotoxin present. The activated enzyme (coagulase) hydrolyses specific bonds within a clotting protein (coagulogen) that is also present in the LAL. Once hydrolysed, the resultant coagulin self-associates and forms a gelatinous clot. The use of LAL for detecting endotoxin evolved from the observation that Gram-negative infection of Limulus polyphemus resulted in fatal intravascular coagulation.