STUDIES ON THE INTERACTION BETWEEN PLASMINOGEN-ACTIVATOR INHIBITOR-1 AND VITRONECTIN

Recently, the functionally active form of plasminogen activator inhibitor type-1 (PAI-1) was found to bind to vitronectin both in plasma and in extracellular matrix. In the present study the formation of the complex between functionally active PAI-1 and vitronectin has been studied using vitronectin-coated microtitre plates. PAI-1 bound to vitronectin in the microtitre plates was quantified using HRP-conjugated monoclonal antibodies towards PAI-1. Even at PAI-1 concentrations of about 1 pmol/l the binding to the vitronectin-coated plates seem to be quantitative suggesting high affinity. In contrast, with 'latent' PAI-1 at similar molar concentrations, no binding was observed. The effects of pH, NaCl, KBr, KSCN, urea, guanidinium chloride and certain amino acids were studied on the interaction between active PAI-1 and vitronectin. The interaction was not affected at a wide pH range or by increasing the ionic strength by addition of NaCl, suggesting that the binding is more complicated than just an ionic binding. In addition, no effect was observed on the complex formation by 2 mol/l KBr. In contrast, 0.5 mol/l KSCN almost completely abolished complex formation. Furthermore, arginine and guanidinium chloride, both dissociated the complex readily. Half maximal binding was obtained at about 0.3 mol/l for both substances. In contrast hardly any effect was obtained with epsilon aminocaproic acid (EACA) or lysine in concentrations up to 1.6 mol/l. Our results suggest that guanidine groups and most likely also hydrophobic interactions are involved in the binding of the active form of PAI-1 to vitronectin.