Functional α2-macroglobulin half-molecules induced by cadmium

Abstract Human α 2 -macroglobulin can be reversibly dissociated by Cd 2+ at low ionic strength in half-molecules which retain their ability to bind tightly plasmin and chymotrypsin. The steady state kinetic parameters of these proteinases towards chromogenic substrates when bound to half-molecules are not greatly different from those determined for these enzymes linked to whole α 2 M molecules. Cd 2+ can also induce the dissociation of plasmin- and chymotrypsin - α 2 M complexes into proteinase-α 2 M half-molecule conjugates. These results, taken with the fact that monomeric units of α 2 M cannot bind these proteinases, strongly suggest that each active site of α 2 M consists in a specific arrangement of two monomeric units linked by disulfide bridges.