Vitamins, Harmones and Hemoglobin
Carboxylation of clotting factors by Vit. K is amino acid γ carboxylation of ?(AIIMS Nov 2008)
a. 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.
b. 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 → -carboxyglutamic acid.
c. The → -carboxyglutamic acid residues are good chelators and allow prothrombin to bind Ca 2+ .
d. The prothrombin –Ca 2+ complex in turn binds to the phospholipid membrane, where proteolytic conversion to thrombin can occur in vivo.
e. 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 .