Vitamin K serves as a coenzyme in reactions that result in the modified activity of several enzymes of the blood coagulation cascade. Which of the following amino acid modifications requires the activity of vitamin K?
A) aspartate to β-carboxyaspartate
B) glutamate to g-carboxyglutamate
C) lysine to hydroxylysine
D) lysine to β-methyllysine
E) proline to hydroxyproline

Question

Quizplus · Accepted Answer

Vitamin K is essential for the carboxylation of glutamate residues to form γ-carboxyglutamate in certain proteins, which is crucial for blood coagulation.  The major function of the K vitamins is in the maintenance of normal levels of the blood-clotting proteins, factors II, VII, IX, X, and protein C and protein S, which are synthesized in the liver as inactive precursor proteins. Conversion from inactive to active clotting factor requires a posttranslational modification of specific glutamate (E) residues. This modification is a carboxylation and the enzyme responsible requires vitamin K as a cofactor. The resultant modified E residues are g-carboxyglutamate (gla)

Vitamin K Serves as a Coenzyme in Reactions That Result