Tissue factor pathway inhibitor

Tissue factor pathway inhibitor (or TFPI) is a single-chain polypeptide which can reversibly inhibit Factor Xa (Xa). While Xa is inhibited, the Xa-TFPI complex can subsequently also inhibit the FVIIa-TF complex. TFPI contributes significantly to the inhibition of Xa in vivo, despite being present at concentrations of only 2.5nM.

Genetics
The gene for TFPI is located on chromosome 2q31-q32.1, and has nine exons which span 70kb. The gene has not been completely sequenced yet. A similar gene, termed TFPI2, has been identified on chromosome 7q22; in addition to TFPI activity, its product also has retinal pigment epithelial cell growth-promoting properties.

Protein structure
TFPI has a relative molecular mass of 34000 to 40000 depending on the degree of proteolysis of the C-terminal region.