The aminoacid carboxylated by vitamin K is
## Core Concept
The question tests the understanding of the role of vitamin K in the carboxylation of amino acids, which is crucial for blood coagulation. Vitamin K acts as a cofactor for the enzyme γ-glutamyl carboxylase. This enzyme is essential for the post-translational modification of certain proteins, notably clotting factors in the liver.
## Why the Correct Answer is Right
The correct answer, **γ-glutamic acid (or glutamate)**, is the amino acid that undergoes carboxylation in a reaction dependent on vitamin K. This process converts glutamate residues to γ-carboxyglutamate (Gla) in proteins such as prothrombin and other clotting factors. The γ-carboxyglutamate residues are critical for the calcium-binding properties of these proteins, which is necessary for their function in blood coagulation.
## Why Each Wrong Option is Incorrect
- **Option A:** While certain amino acids can be modified post-translationally, **alanine** is not specifically known for carboxylation by a vitamin K-dependent process.
- **Option B:** **Aspartic acid** can undergo various modifications, but it is not the specific target for vitamin K-dependent carboxylation.
- **Option D:** **Lysine** is involved in different types of post-translational modifications, such as cross-linking in collagen or being a target for certain enzymes, but not vitamin K-dependent carboxylation.
## Clinical Pearl / High-Yield Fact
A key clinical point to remember is that **warfarin**, an anticoagulant, works by inhibiting the synthesis of vitamin K-dependent clotting factors (II, VII, IX, and X) through the blockade of vitamin K recycling. This results in reduced γ-carboxylation of glutamate residues in these proteins, impairing their function in blood coagulation.
## Correct Answer: C. γ-glutamic acid.