Platelets produce which enzyme that converts prothrombin to thrombin?

Platelets produce which enzyme that converts prothrombin to thrombin?

• A. Thromboplastin
• B. Prothrombinase
• C. Fibrinogen
• D. Platelet factor 4

Answer: (A)

Platelets provide the surface where the prothrombinase complex forms, and that complex is the enzyme that converts prothrombin to thrombin. Prothrombinase consists of factor Xa and factor Va, with calcium and platelet phospholipids on the platelet membrane. Platelets don’t produce thromboplastin; thromboplastin (tissue factor) initiates the extrinsic pathway and comes from damaged tissue, not platelets. Fibrinogen is the thrombin substrate, cleaved to form fibrin, and platelet factor 4 is a platelet granule protein with other roles, not the enzyme that activates prothrombin.

Platelets provide the surface where the prothrombinase complex forms, and that complex is the enzyme that converts prothrombin to thrombin. Prothrombinase consists of factor Xa and factor Va, with calcium and platelet phospholipids on the platelet membrane. Platelets don’t produce thromboplastin; thromboplastin (tissue factor) initiates the extrinsic pathway and comes from damaged tissue, not platelets. Fibrinogen is the thrombin substrate, cleaved to form fibrin, and platelet factor 4 is a platelet granule protein with other roles, not the enzyme that activates prothrombin.