Vitamin K acts as a cofactor for carboxylase, which causes post-translational t modification of coagulation factors II (prothrombin), VII, IX, and X, and of plasma regulatory proteins, proteins C and S.
Vitamin K-dependent coagulation factors or zymogens are a group of calcium-binding proteins. They are characterised by a -NH2 terminal G1a domain that contains 10-12 gamma-carboxyglutamate residues. Vitamin K acts as a cofactor for the carboxylase involved in the conversion of NH2-terminal glutamic acid residues to the gamma-carboxyglutamate residues in these proteins.
The primary site of synthesis of vitamin K-dependent proteins of the blood is in the liver. They are synthesised in a non-functional precursor form (pre-proenzymes), reduced vitamin K being required for activation.
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