The phospholipid requirement of tissue factor in blood coagulation.

Using a coagulation assay specific for tissue factor, we found that removal of 95% of the tissue factor-phospholipid resulted in a loss of 98% of its biological activity. The activity could be restored, with yields in excess of 100% by combining the extracted tissue factor with either mixed brain phospholipids or highly purified phospholipids. Phosphatidylethanolamine was the most active, followed by phosphatidylcholine. Phosphatidylserine, phosphatidylinositol, and sphingomyelin had little or no activity. In addition, a requirement for unsaturation and the presence of two fatty acids was demonstrated. The activity of phosphatidylcholine was also dependent on the presence of the base. Furthermore, it was shown that activity was not a function of binding of phospholipids to tissue factor, as both active and inactive lipids were equally bound.