The use of alpha 2-antiplasmin as a model for the demonstration of complex reversibility in serpins

Human alpha 2-antiplasmin readily forms 1:1 complexes with either trypsin or chymotrypsin at independent but overlapping reactive sites. In the absence of alpha 2-macroglobulin, complex dissociation and enzyme release can be demonstrated without regeneration of inhibitory activity. However, in the presence of this inhibitor the dissociation of alpha 2-antiplasmin-chymotrypsin complexes or alpha 2-antiplasmin-trypsin complexs yields functionally active inhibitors which can now inactivate trypsin and chymotrypsin, respectively. These results clearly indicate that Serpin-proteinase complexes can dissociate to give both active inhibitor and enzyme. If the enzyme is trapped by alpha 2-macroglobulin, in vivo, it is possible that the inhibitor may be recycled for further use.