Proteinase binding and inhibition by the monomeric alpha -macroglobulin rat alpha sub(1)-inhibitor-3

The inhibitory capacity of the alpha -macroglobulins resides in their ability to entrap proteinase molecules and thereby hinder the access of high molecular weight substrates to the proteinase active site. This ability is thought to require at least two alpha -macroglobulin subunits, yet the monomeric alpha -macroglobulin rat alpha sub(1)-inhibitor-3 ( alpha sub(1)I sub(3)) also inhibits proteinases. The authors have compared the inhibitory activity of alpha sub(1)I sub(3) with the tetrameric human homolog alpha sub(2)-macroglobulin ( alpha sub(2)M), the best known alpha -macroglobulin, in order to determine whether these inhibitors share a common mechanism.