| Abstrakt: |
Alpha2-macroglobulin, a protease-binding protein that is reactive with almost all endopeptidases, is present in high concentrations in the plasma of the horseshoe crab, Limulus. Alpha2-macroglobulin was demonstrated by its ability to protect the active site of trypsin from inactivation by the macromolecular active site inhibitor, soybean trypsin inhibitor, and by reaction with an antiserum prepared against purified Limulusα2-macroglobulin. The blood cells also contain α2-macroglobulin in a form that is released when washed cells are stimulated to undergo exocytosis by treatment with the ionophore, A23187. Alpha2-macroglobulin is detected in the materials released from the cells during degranulation both by activity in the soybean trypsin inhibitor-protection assay and by immunochemical staining of Western blots. The subunit molecular weight of the cell-associated form of α2-macroglobulin, 185 kDa, is identical to that of the plasma form. The amount of α2-macroglobulin contained within the cells of a given volume of blood is 0.5-2% of the quantity in solution in that volume of plasma. The distilled water lysates of N-ethylmaleimide-stabilized amebocytes used to detect endotoxin (e.g., Limulusamebocyte lysate or LAL) contain relatively large quantities of active α2-macroglobulin. These preparations are essentially free of the principal plasma protein, hemocyanin, indicating that the cells had been well washed prior to lysis. |
