Enzyme complexes containing native tissue factor versus portable tissue factor. Native tissue factor contains a transmembrane tail that anchors it to the membrane. Portable tissue factor is a soluble, engineered protein that uses annexin V to come to a phosphatidylserine-containing membrane. Exposed phosphatidylserine enhances binding of factor VIIa to tissue factor and of factor X to the complex of factor VIIa with tissue factor. Illustration by Paulette Dennis.