endopeptidase inhibitor activity obsolete alpha-2 macroglobulin true OBSOLETE. Inhibition of proteinase by a mechanism involving a bait region which contains specific sites, cleavage of which induces a conformational change that results in trapping of the proteinase; following cleavage in the bait region a thiolester bond is hydrolyzed and mediates the covalent binding of the protein to the proteinase; subsequently epsilon-amino groups of the proteinase react with thiolester linkages in the inhibitor to form stable amide links; the entrapped proteinase can now only act on low molecular mass substrates. This term was made obsolete because it represents a gene product. molecular_function GO:0016975 alpha-2 macroglobulin