title: An endopeptidase inhibitor, similar to mammalian alpha 2-macroglobulin, detected in the hemolymph of an invertebrate, Limulus polyphemus.
abstract: A protease inhibitory activity has been detected in the hemolymph of the horseshoe crab, Limulus polyphemus. The inhibitor possesses many of the characteristics of vertebrate alpha 2-macroglobulin. The inhibitor, found in the high speed supernatant of Limulus plasma, is sensitive to mild acidification, inhibits a variety of prokaryotic and eukaryotic endopeptidases, and is sensitive to methylamine treatment. Although the inhibitor completely prevents the trypsin-mediated hydrolysis of protein substrates, the hydrolysis of a low molecular substrate by trypsin is unaffected by the inhibitor, a property characteristic of alpha 2-macroglobulin. The striking similarity of the inhibitor to vertebrate alpha 2-macroglobulin, coupled with the fossil record of Limulus, suggests that such protease inhibitors are ancient molecules.
mesh_terms: D000818:Animals; D006458:Hemolymph / Q000032:analysis*; D006737:Horseshoe Crabs; D007700:Kinetics; D011480:Protease Inhibitors / Q000302:isolation & purification*; D013379:Substrate Specificity; D014357:Trypsin / Q000378:metabolism*; D014361:Trypsin Inhibitors / Q000302:isolation & purification; D000511:alpha-Macroglobulins
chemical_list: D011480:Protease Inhibitors; D014361:Trypsin Inhibitors; D000511:alpha-Macroglobulins; D014357:Trypsin