Interaction of cY,-Macroglobulin with Trypsin, Chymotrypsin, Plasmin, and Papain’

The interaction ae-macroglobulin with four proteinases has been investigated by binding assays and by gel electrophoresis. At pH 7.65 the binding ratios of the proteinase-cwa-macroglobulin complexes were found to be 2:l (trypsin and papain), 1.4:1 (chymotrypsin), and 1:l (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 az-macroglobulin peptide chains. Rate studies have shown that the relative rates of reaction of the proteinases with (Yemacroglobulin also varied greatly: papain > trypsin > chymotrypsin > 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 ae-macroglobulin and cleave the second pair of scissile cuz-macroglobulin peptide bonds before the ae-macroglobulin has undergone the conformational change initiated by the formation of the 1:l proteinase a2-macroglobulin complex.