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Functional properties of an endothelial cell cofactor for thrombin-catalyzed activation of protein C.

Authors
  • Owen, W G
  • Esmon, C T
Type
Published Article
Journal
The Journal of biological chemistry
Publication Date
Jun 10, 1981
Volume
256
Issue
11
Pages
5532–5535
Identifiers
PMID: 6894592
Source
Medline
License
Unknown

Abstract

Thrombin-catalyzed activation of Protein C is accelerated by a human endothelial cell surface cofactor. The cofactor occurs also on mouse hemangioma cells (a transformed endothelial cell line), but not on cultured human smooth muscle cells or fibroblasts. The cofactor remains bound to the cell surface during Protein C activation. The cofactor is saturable with respect to both Protein C (Km = 0.72 +/- 0.07 microM) and thrombin (Km = 0.48 +/- 0.05 nM). Diisopropylphosphoryl-thrombin is a competitive inhibitor of the cofactor-dependent reaction with Ki = 0.56 +/- 0.1 nM. Prothrombin Fragment 1, the peptide derived from prothrombin that retains phospholipid binding capacity, does not inhibit activation of Protein C when present in a 7:1 molar excess over Protein C. Platelet Factor 4 (20 microgram/ml) also fails to inhibit Protein C activation. It is concluded that the endothelial cell provides a surface on which Protein C can be activated under physiological conditions.

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