Complex formation between plasminogen activator inhibitor 1 and vitronectin in purified systems and in plasma

Functionally active PAI-1 is bound to a discrete binding or carrier protein in plasma, which was recently identified as vitronectin. In the present study, the interaction between PAI-1 and vitronectin has been studied in purified systems and in plasma by agarose gel electrophoresis using non-denaturing conditions and by crossed immunoelectrophoresis using an antiserum produced towards purified PAI-1/vitronectin complex. Both methods revealed a clearly distinguishable complex with electrophoretic mobility in between the parent molecules. Virtually all of the purified vitronectin, which did not contain any appreciable amounts of polymerized material, and almost all of the vitronectin in plasma, had the capacity to form a complex with PAI-1. The results suggested a stoichiometry of 1:1 as the most likely ratio between the two molecules in the complex. In contrast to functionally active PAI-1, latent or chloramine T-inactivated PAI-1 did not form such a complex with vitronectin.