Plasminogen activator inhibitor type-1: reactive center and amino-terminal heterogeneity determined by protein and cDNA sequencing.

Both the urokinase-type and tissue-type plasminogen activator can convert their approximately 54 kDa type-1 inhibitor (PAI-1) to an inactive form with a lower apparent molecular mass. We have determined the amino-terminal amino acid sequences of human native and converted PAI-1, and isolated PAI-1 cDNA and determined the nucleotide sequence in regions corresponding to the amino-terminus and the cleavage site. The data show that the conversion of the inhibitor consists of cleavage of an Arg-Met bond 33 residues from the carboxy-terminus, thus localizing the reactive center of the inhibitor to that position. In addition, a heterogeneity was found at the amino-terminus, with a Ser-Ala-Val-His-His form and a two-residue shorter form (Val-His-His-) occurring in approximately equal quantities.