The C-terminus of tissue factor pathway inhibitor is essential to its anticoagulant activity.

Tissue factor pathway inhibitor (TFPI) from different cell lines shows up to 15-fold differences in the ratio of anticoagulant to chromogenic activity. The anticoagulant activity was dependent on the purification procedure used and it was possible to isolate two fractions of recombinant TFPI. Only one of these fractions showed anticoagulant activity comparable with TFPI from normal human plasma, and Western blotting showed that the low-activity fraction did not react with an antibody raised against a peptide of TFPI located near the C-terminal. Analysis by mass spectroscopy of peptides from V8 protease digests showed that C-terminal amino acids could only be identified from the high-activity form, while heterologous fragmentation had taken place in the form with low anticoagulant activity. Previously published studies on TFPI have been performed using material of low anticoagulant activity compared with plasma TFPI, and we suggest that these studies have been performed with material degraded in the C-terminus.