Figure 2. Mechanism for heparin inhibition of the intrinsic tenase complex. Factor IXa (pink) and factor VIIIa (blue) are assembled on the phospholipids surface. The domain structures of FIXa (Gla, EGF1, EGF2, and protease) and FVIIIa (A1, A2, and A3-C1-C2) are labeled with putative FVIIIa interactive sites on FIXa (highlighted yellow). Heparin oligosaccharide bound to the C-terminal alpha helix of FIXa is represented with a thick red chain that displaces the FVIIIa A2 domain.