Thromboplastin (TPL) is derived from cell membranes and is a mixture of both phospholipids and tissue factor, neither of which are enzymes.
Thromboplastin acts on and accelerates the activity of Factor Xa, also known as thrombokinase,[1] aiding blood coagulation through catalyzing the conversion of prothrombin to thrombin.
Historically, thromboplastin was a lab reagent, usually derived from placental sources, used to assay prothrombin times (PT).
Thromboplastin is the combination of both phospholipids and tissue factor, both of which are needed in the activation of the extrinsic pathway.
Complete thromboplastin consists of tissue factor, phospholipids (since platelets were removed from blood sample being tested), and CaCl2 to reintroduce calcium ions which were chelated by sodium citrate originally used to prevent coagulation of the sample blood during transportation and/or storage.