Coagulogens from four living species of horseshoe crabs (Limulidae): comparison of their biochemical and immunochemical properties.

Coagulogens from four kinds of horseshoe crabs (Limulus polyphemus (LP), Tachypleus tridentatus (TT), Tachypleus gigas (TG), and Carcinoscorpius rotundicauda (CR)) were compared in biochemical and immunochemical properties. On SDS-polyacrylamide gel electrophoresis, the reduced coagulogens had a common apparent molecular weight of 20,000, whereas the molecular weights of unreduced samples were 24,000 for the LP protein and 21,000 for the proteins of the three Asian species (TT, TG, and CR). Gel-filtration yielded apparent molecular weights of 19,500 for the LP protein and 15,500 for the other proteins. All coagulogens consisted of 173-175 amino acid residues and their compositions were very similar to one another, e.g., no methionine, and high proportions of basic amino acids, cystine, valine, and phenylalanine. The amino-terminal 14-residue sequence of the LP coagulogen was Gly-Asp-Pro-Asn-Val-Pro-Thr-Cys-Leu-Cys-Glu-Glu-Pro-Thr. Those of the other coagulogens, Ala-Asp-Thr-Asn-Ala-Pro-Ile-Cys-Leu-Cys-Asp-Glu-Pro-Gly, were identical to one another except for the amino-terminal aspartic acid residue of the TG protein and leucine of the CR protein. The carboxyl-terminal residues of the coagulogens were identified as serine (LP), phenylalanine (TT and TG), and tyrosine (CR), respectively. An antiserum to the LP coagulogen produced a single precipitin line against the LP protein but none against the Asian coagulogens. On the other hand, each of the antiserums to TT, TG, and CR coagulogens yielded a precipitin line against the Asian proteins but gave no line against the LP protein.