Question

The deficiency of which of the following vitamin prevents blood clotting?

• A. Vitamin A
• B. Vitamin K
• C. Vitamin C
• D. Vitamin $B_{12}$

Answer 1

The correct option is B Vitamin K

Vitamin K is a necessary participant in synthesis of several proteins that mediate both coagulation and anticoagulation. Vitamin K deficiency is manifest as a tendency to bleed excessively. Indeed, many commercially-available rodent poisons are compounds that interfere with vitamin K and kill by inducing lethal hemorrhage. Vitamin K serves as an essential cofactor for a carboxylase that catalyzes carboxylation of glutamic acid residues on vitamin K-dependent proteins. The key vitamin K-dependent proteins include:

Coagulation proteins: factors II (prothrombin), VII, IX and X.

Anticoagulation proteins: proteins C, S and Z.

Others: bone proteins osteocalcin and matrix-Gla protein and certain ribosomal proteins.

These proteins have in common the requirement to be post-translationally modified by carboxylation of glutamic acid residues (forming gamma-carboxyglutamic acid) in order to become biologically active. Prothrombin, for example, has 10 glutamic acids in the amino-terminal region of the protein which are carboxylated. Without vitamin K, the carboxylation does not occur and the proteins that are synthesized are biologically inactive.

Therefore, the correct answer is option B.