Prothrombin

Prothrombin is a coagulation (clotting) factor. It is needed for the normal clotting of blood. There is a cascade of biochemical events that leads to the formation of the final clot. In this cascade, prothrombin is a precursor to thrombin. Because prothrombin comes before thrombin, it is called prothrombin. The prothrombin time is a clotting test. A test done to test the integrity of part of the clotting scheme. Familiarly called the "pro time," the test is the time needed for clot formation after a substance called thromboplastin (+ calcium) has been added to plasma. Prothrombin is also known as thrombinogen.

* * *

A glycoprotein, molecular weight approximately 72,500, formed and stored in the parenchymal cells of the liver and present in blood in a concentration of approximately 20 mg/100 mL. In the presence of thromboplastin and calcium ion, p. is converted to thrombin, which in turn converts fibrinogen to fibrin, this process resulting in coagulation of blood; a deficiency of p. leads to impaired blood coagulation. SYN: serozyme, thrombinogen, thrombogen.

* * *

pro·throm·bin (')prō-'thräm-bən n a plasma protein produced in the liver in the presence of vitamin K and converted into thrombin by the action of various activators (as thromboplastin) in the clotting of blood

pro·throm·bic -bik adj

* * *

n.

a substance, present in blood plasma, that is the inactive precursor from which the enzyme thrombin is derived during the process of blood coagulation. See also coagulation factors.

* * *

pro·throm·bin (pro-thromґbin) [pro- + thrombo- + -in chemical suffix] factor II; see under coagulation factors, at factor.