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Protein Z is a member of the coagulation cascade, the group of blood proteins that leads to the formation of blood clots. It is vitamin K-dependent, and its functionality is therefore impaired in warfarin therapy. It is a glycoprotein.
Although it is not enzymatically active, it is structurally related to several serine proteases of the coagulation cascade: factors VII, IX, X and protein C. The carboxyglutamate residues (which require vitamin K) bind protein Z to phospholipid surfaces.
The main role of protein Z appears to be the degradation of factor Xa. This is done by protein Z-related protease inhibitor (ZPI), but the reaction is accelerated 1000-fold by the presence of protein Z. Oddly, ZPI also degrades factor XI, but this reaction does not require the presence of protein Z.
In some studies, deficiency states have been associated with a propensity to thrombosis. Others, however, link it to bleeding tendency; there is no clear explanation for this, as it acts physiologically as an inhibitor, and deficiency would logically have led to a predisposition for thrombosis.
- ^ Prowse CV, Esnouf MP. The isolation of a new warfarin-sensitive protein from bovine plasma. Biochem Soc Trans 1977;5:255-256. PMID 892175.
- ^ Broze GJ Jr, Miletich JP. Human Protein Z. J Clin Invest 1984;73:933-8. PMID 6707212.
|Coagulation factors||intrinsic pathway (FXII, FXI, FIX, FVIII) - extrinsic pathway (Tissue factor, FVII) - common pathway (FX, FV, (Pro)thrombin / FII, Fibrin / FI, FXIII) - HMWK - vWF - Kallikrein|
|Inhibitors||Antithrombin - Protein C - Protein S - Protein Z - ZPI - TFPI|
|Fibrinolysis||Plasmin - tPA/urokinase - PAI-1/2 - α2-AP - α2-macroglobulin - TAFI|