Which of the following statements about vitamin K is correct?
A) Vitamin K is obtained commercially from rats.
B) It is a water soluble vitamin.
C) It is a cofactor for an enzyme which carboxylates glutamate residues in proteins.
D) When bound to activated prothrombin, vitamin K provides a binding site for calcium ions.
E) When in the diet, it enhances the uptake of iron.

Question

Quizplus · Accepted Answer

Vitamin K acts as a cofactor for the enzyme gamma-glutamyl carboxylase, which carboxylates (adds a carboxyl group to) glutamate residues in proteins, including blood clotting factors. This carboxylation is important for the proper function of these proteins. Vitamin K is a fat-soluble vitamin, meaning it is not easily excreted from the body and can accumulate to toxic levels if consumed in excess. Vitamin K is derived from plant sources such as leafy greens, and is not obtained commercially from rats. Vitamin K does not provide a binding site for calcium ions when bound to activated prothrombin, and it does not enhance the uptake of iron.

Which of the Following Statements About Vitamin K Is Correct