Platelet coagulation factor XIa-inhibitor, a form of Alzheimer amyloid precursor protein.
An inhibitor of coagulation factor XIa was purified from serum-free conditioned medium of HepG2 liver cells. Platelets stimulated with thrombin or calcium ionophore (A23187) secrete a protein functionally and immunologically identical to the inhibitor, implying a role for this inhibitor in hemostasis. Analysis of the amino-terminal amino acid sequence and immunologic reactivity showed the inhibitor to be a truncated form of the Alzheimer's amyloid precursor protein that contains a Kunitz-type serine protease inhibitor domain and at least a portion of the amyloid beta protein. It inhibits factor XIa and trypsin with a Ki of 450 +/- 50 pM and 20 +/- 10 pM, respectively. Heparin (1 unit/ml) did not significantly effect inhibition of trypsin, but inhibition of XIa was 15 times greater ( Ki = 25 +/- 15 pM) in the presence of heparin.[1]References
- Platelet coagulation factor XIa-inhibitor, a form of Alzheimer amyloid precursor protein. Smith, R.P., Higuchi, D.A., Broze, G.J. Science (1990) [Pubmed]
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