title: Interaction of alpha 2-macroglobulin with trypsin, chymotrypsin, plasmin, and papain.
abstract: The interaction alpha 2-macroglobulin with four proteinases has been investigated by binding assays and by gel electrophoresis. At pH 7.65 the binding ratios of the proteinase-alpha 2-macroglobulin complexes were found to be 2:1 (trypsin and papain), 1.4:1 (chymotrypsin), and 1:1 (plasmin). The progressive decrease in the stoichiometry of the three seryl proteinase complexes was paralleled by a concomitant decrease in the proteinase-dependent specific cleavage of the alpha 2-macroglobulin peptide chains. Rate studies have shown that the relative rates of reaction of the proteinases with alpha 2-macroglobulin also varied greatly: papain greater than trypsin greater than chymotrypsin greater than plasmin. The data suggest that the ability of a proteinase to saturate the second proteinase binding site is a reflection of its ability to bind to alpha 2-macroglobulin and cleave the second pair of scissile alpha 2-macroglobulin peptide bonds before the alpha 2-macroglobulin has undergone the conformational change initiated by the formation of the 1:1 proteinase alpha 2-macroglobulin complex.
mesh_terms: D002918:Chymotrypsin / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D005341:Fibrinolysin / Q000032:analysis*; D010206:Papain / Q000032:analysis*; D011485:Protein Binding; D014357:Trypsin / Q000032:analysis*; D000511:alpha-Macroglobulins / Q000032:analysis*
chemical_list: D000511:alpha-Macroglobulins; D002918:Chymotrypsin; D014357:Trypsin; D005341:Fibrinolysin; D010206:Papain