| abstract |
The present invention provides a technique relating to a horseshoe crab factor B variant and, in its turn, provides a means for highly sensitively assaying an endotoxin. A polypeptide having an amino acid sequence, in which the amino acid residue at the 193-position in the amino acid sequence of horseshoe crab factor B polypeptide is substituted into a cysteine (Cys) residue, is produced. By preparing a Limulus reagent using a combination of the thus obtained polypeptide with horseshoe crab factor C, an endotoxin can be assayed at a high sensitivity. |