This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
Dicumarol is a drug that impairs the utilization of vitamin K by the liver. Dicumarol therapy, therefore, would decrease the plasma concentration of which of the following procoagulants? 
Select and explain. 
A. Prothrombin, B. Fibrinogen, C. Factor XI, D. Ac-globulin (factor V)
A: Prothrombin
Answer: A: Prothrombin 
Explanation: Dicumarol inhibits the action of vitamin K, which is a necessary cofactor for the enzyme that catalyzes the conversion of glutamic acid residues to g-carboxyglutamic acid residues.Six of the proteins involved in clotting require conversion of a number of glutamic acid residues to g-carboxyglutamic acid residues before being released into the circulation, and hence all six are vitamin K-dependent. These proteins include factors II (prothrombin)Others are; factors VII, IX, and X, protein C, and protein S Ref: Ganong's Review of Medical Physiology Twenty-Third Edition Page No: 535