Human blood coagulation factor VII circulates in blood as a precursor of a serine protease. The expression of the proteolytic activity of factor VII, or its activated form, factor VIIa, occurs as a result of complex formation with a specific tissue lipo-protein designated tissue factor. While many of the steps involved in coagulation have been studied on a biochemical basis, little is known as to the mechanism whereby the activity of factor VII towards protein substrates is augmented several orders of magnitude by complex formation with tissue factor in the presence of calcium ions.
The specific aims of the proposed research are: (a) to biochemically characterize human blood clotting factor VII, (b) to study the mechanism of activation of factor VII by a number of purified coagulation proteases as well as by crude homogenates of endothelial cells, monocytes, macrophages and platelets, (c) to study the interaction, procoagulant activity and substrate specificity of human factor VIIa on cultured endothelial cells in both the quiescent and perturbed states, and (d) to isolate and fully characterize a tissue factor from human brain tissue, and determine the kinetic impact of purified tissue factor on the proteolytic activity and inhibitory sensitivity of factor VII and factor VIIa. One of the long-range goals of this project is to compare, biochemically and immunochemically, tissue factor isolated from brain tissue with tissue factor found in the vascular endothelium and subendothelium, as well as in atherosclerotic plaques. The proposed research will utilize standard isolation and characterization procedures, established coagulation assays, analytical and preparative electrophoresis, affinity chromatography and amino acid sequence methodology. Hopefully, information gathered in this study will provide insight into the precise role of factor VII in both normal and pathological states, and inferences as to the role of coagulation in atherosclerosis as a consequence of repetitive plaque rupture, release or exposure of tissue factor, and incidental coagulation at the rupture site.
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