title: Tissue factor pathway inhibitor
text: # 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-tissue factor complex. TFPI contributes significantly to the inhibition of Xa in vivo, despite being present at concentrations of only 2.5 nM.
  
  ## Genetics
  
  The gene for TFPI is located on chromosome 2q31-q32.1, and has nine exons which span 70 kb. A similar gene, termed TFPI2, has been identified on chromosome 7, at locus 7q21.3; 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 34,000 to 40,000 depending on the degree of proteolysis of the C-terminal region.
  
  TFPI consists of a highly negatively charged amino-terminus, three tandemly linked Kunitz domains, and a highly positively charged carboxy-terminus. With its Kunitz domains, TFPI exhibits significant homology with human inter-alpha-trypsin inhibitor and bovine basic pancreatic trypsin inhibitor.
  
  ## Interactions
  
  Tissue factor pathway inhibitor has been shown to interact with Factor X.
  
  