Protein C deficiency in liver disease.

Protein C is a vitamin K-dependent zymogen of a serine protease that is found in blood plasma. The active form, activated protein C, can inhibit blood coagulation and stimulate fibrinolysis. Protein C is synthesized in the liver as a single chain protein. Its synthesis requires several post-translational modifications including carboxylation of glutamic acid residues, hydroxylation of aspartic acid residues, and glycosylation. Plasma protein C levels are sensitive to liver function. Protein C levels fall more rapidly than other vitamin K-dependent proteins when synthesis is altered by the administration of oral anticoagulants. In addition, low protein C levels are highly indicative of abnormal liver function. In one case, homozygous protein C deficiency has been corrected by liver transplantation. In liver transplantation for end-stage liver failure, plasma protein C levels may be a good indicator of the success of the transplantation.