THE ACTIVITY OF PLASMINOGEN-ACTIVATOR INHIBITOR-1 (PAI-1) OF HUMAN PLATELET

We have previously shown that platelets account for 93% of circulating PAI-1 antigen but for only half the PAI activity, suggesting that platelet PAI-1 is less active than plasma PAI-1. Here we show, both by an assay for the PAI-1 that is capable of forming a complex with t-PA and by a chromogenic assay for PAI activity, that human platelet PAI-1 is 3.5 ± 1.1% active. Human PAI-1, purified either from platelets or endothelial cells, was reactivated by 4M guanidine to a final specific activity of about 300,000 U/mg PAI-1. © 1990.