Which amino acid residues gets carboxylated by vitamin K during post translational modification
**Core Concept**
The underlying principle being tested is the role of **vitamin K** in the post-translational modification of proteins, specifically in the process of **carboxylation**. This process is crucial for the activation of certain proteins involved in **blood coagulation**. The carboxylation of specific amino acid residues is essential for the binding of these proteins to **calcium ions**.
**Why the Correct Answer is Right**
The correct answer involves the carboxylation of **glutamic acid residues** by vitamin K. This process, also known as gamma-carboxylation, converts glutamic acid residues into **gamma-carboxyglutamic acid (Gla)**, which is essential for the biological activity of proteins such as **prothrombin** and other **clotting factors**. Vitamin K serves as a cofactor for the enzyme **gamma-glutamyl carboxylase**, which catalyzes this reaction.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while aspartic acid is an amino acid with a carboxyl group, it is not the target of vitamin K-dependent carboxylation.
**Option B:** Incorrect as it is not directly related to the question.
**Option D:** Incorrect as it does not specify the correct amino acid residue.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **warfarin**, a common anticoagulant, acts by inhibiting the enzyme **vitamin K epoxide reductase**, thereby reducing the availability of vitamin K for carboxylation reactions and leading to a decrease in the production of active clotting factors.
**Correct Answer:** D. Glutamic acid.