Alpha 2 macroglobulin is a serum protein which is mainly synthesised in the liver. It functions as a broad range irreversible proteinase inhibitor that forms a "trap" around most proteases. Alpha 2 macroglobulin is is a tetrameric molecule, and with a molecular weight of 720 kDa, it so large a molecule that it tends to remain intravascular. Following conformational change, the protinase is deposited within a central cavity where it is still active but prevented from further contact with its substrate. Removal of the complex is mediated by the generation of recognition sites which react with receptors on a variety of cells including macrophages and liver cells. Alpha 2 macroglobulin is localized on the surface of peripheral blood lymphocytes.