 Cytosolic PAI-2 tends to be monomeric, while PAI-2 in secretory organelles (which tend to be more oxidizing than the cytosol) is more prone to polymerization.For these combined reasons, it is thought that PAI-2 may sense and respond to environmental redox potential.PAI-2 uses a suicide inhibition mechanism (a common mechanism for serpins) to irreversibly inactivate tPA and urokinase.