(= a-2-macroglobulin)Large (725 kD) plasma antiprotease with very broad spectrum of inhibitory activity against all classes of proteases. Apparently works by trapping the protease within a cage that closes when the protease-sensitive bait sequence is cleaved. The protease is still active against small substrates that can diffuse into the cage, and the conformational change that closes the trap alters the properties of the a -2-macroglobulin molecule so that it is rapidly removed from circulation. Plasminogen activator is one of the few proteases against which a -2-macroglobulin is ineffective.
Dictionary of molecular biology. 2004.