A Comparison of Plasma and Serum Factor VII Activity and the Formation of Tissue Thromboplastin

Summary 1. A mixture of human serum or plasma and bovine plasma free of factors VII and X gave, with human brain extract, identical clotting times. 2. An assay of factor VII in materials low in prothrombin using human plasma euglobulin was devised. 3. Factor VII isolated from human plasma or serum gave similar activity with human brain extract. 4. From a preparation containing factors VII and X which was added to human brain extract in the average 31% factor VII and 25% factor X was recovered. This was not dependent on the activity of factors VII and X in the original preparation. This indicates that factors VII and X are in equilibrium with tissue thromboplastin. 5. Factors VII and X are not species specific but a higher concentration of these factors is required for prothrombin conversion in a heterologous reaction mixture. 6. Factor VII activity is identical in silicone-coated or uncoated glass surfaces.