 When PAI-2 is in its monomeric form, the CD-loop is vastly out-of-position for this disulfide linkage, and it must translocate a distance of 54 Å to become sufficiently close to Cys-161.Nevertheless, since the CD-loop is quite flexible, the monomeric and polymerigenic forms are fully interconvertible, and one state can be favored over the other by altering the redox environment of the protein.Polymerization of PAI-2 occurs spontaneously under physiological conditions, for instance in the cytosol of placental cells.