Whether PAI-2's physiological function is inhibition of the extracellular protease urokinase and/or whether PAI-2 has intracellular activities remains controversial.

This CD-loop is particularly flexible and difficult to stabilize, as the loop is known to translocate up to 54 Å during the formation of intramolecular disulfide bonds.

[8] In addition to the CD-loop, notable motifs include the reactive center loop (RCL) spanning amino acids 379-383 and an N-terminal hydrophobic signal sequence.

[11] 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.

During pregnancy, PAI-2 is particularly present in the decidua and amniotic fluid, where it may protect membranes from digestion and aid in remodeling fetal and uterine tissues.

[16] PAI-2 plays a role in inflammatory responses and infections, potentially in downregulating T cells that secrete IgG2c and interferon type II.

[16] Due to its position on chromosome 18 close to the bcl-2 protooncogene and several other serpins, PAI-2's role in apoptosis has been investigated, but current evidence remains inconclusive.

This protection is particularly salient in brain metastases, which tend to express high levels of PAI-2 and neuroserpin, and whose growth may be partially inhibited by knockout of PAI-2.