Carboxylation of clotting factors by vitamin K isrequired to be biologically active. Which of the following amino acid is carboxylated?
**Core Concept**
Vitamin K-dependent clotting factors require post-translational modification, specifically carboxylation of specific amino acids, to enable their biological activity. This process involves the conversion of glutamate residues to gamma-carboxyglutamate (Gla), which is essential for the binding of calcium ions and subsequent activation of these proteins.
**Why the Correct Answer is Right**
The correct answer is glutamate because it is the amino acid that undergoes carboxylation in vitamin K-dependent clotting factors. This process is mediated by the enzyme gamma-glutamyl carboxylase, which uses vitamin K as a cofactor to introduce a carboxyl group onto the glutamate residue. This modification is crucial for the activation of clotting factors II, VII, IX, and X, as well as protein C and protein S.
**Why Each Wrong Option is Incorrect**
* **Option A:** There is no information about asparagine being carboxylated in vitamin K-dependent clotting factors.
* **Option B:** Serine is not the amino acid that undergoes carboxylation in vitamin K-dependent clotting factors.
* **Option D:** There is no information about valine being carboxylated in vitamin K-dependent clotting factors.
**Clinical Pearl / High-Yield Fact**
Vitamin K-dependent clotting factors must undergo carboxylation of glutamate residues to become biologically active. This process is essential for the proper functioning of these proteins in the coagulation cascade.
**Correct Answer:** C. Glutamate.