Gamma carboxylation of glutamic acid in clotting factors II, VII and protein C is dependent on
A. Vitamin KB. Vitamin C
C. Vitamin A
D. Vitamin E
Ans. A. (Vitamin K)
Explanation
•Vitamin K is required for the conversion of several clotting factors and prothrombin precursors to the active state. The mechanism of this action has been most clearly delineated for prothrombin.
•Vitamin K is required for the conversion of several clotting factors and prothrombin precursors to the active state. The mechanism of this action has been most clearly delineated for prothrombin.
•Prothrombin
is synthesized as an inactive precursor called pre-prothrombin. Conversion to
the active form requires a vitamin K-dependent carboxylation of specific
glutamic acid residues to y-carboxyglutamic acid.
•The
‘y-carboxyglutamic acid residues are good chelators and allow prothrombin to
bind Ca2.
•The
prothrombin—Ca2 complex in turn binds to the phospholipid membrane, where
proteolytic conversion to thrombin can occur in vivo.
•Factors
2, 7, 9 and 10 are synthesized in the liver as inactive precursors. They
undergo post-translational modification: gamma carboxylation of glutamic
residues. This step is Vitamin K dependant.
