This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
[{'content': 'Which vitamin is required for carboxylation of clotting factors? rpt Q33 \nSelect and explain. \nA. Vitamin A, B. Vitamin D, C. Vitamin E, D. Vitamin K', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The principal role of vitamin K is in the posttranslational modification of various blood clotting factors, in which it serves as a coenzyme in the carboxylation of ceain glutamic acid residues present in these proteins. Vitamin K exists in several forms, for example, in plants as phylloquinone (or vitamin K1), and in intestinal bacterial flora as menaquinone (or vitamin K2). A synthetic form of vitamin K, menadione, is available.Function of vitamin K 1. Formation of g-carboxyglutamate (GLA): Vitamin K is required in the hepatic synthesis of prothrombin and blood clotting factors II, VII, IX, and X. These proteins are synthesized as inactive precursor molecules. Formation of the clotting factors requires the vitamin K-dependent carboxylation of glutamic acid residues to Gla residues (Figure 28.26). This forms a mature clotting factor that contains Gla and is capable of subsequent activation. The reaction requires O2, CO2, and the hydroquinone form of vitamin K. The formation of GLA is sensitive to inhibition by dicumarol, an anticoagulant occurring naturally in spoiled sweet clover, and by warfarin, a synthetic analog of vitamin K.Ref: Lippincott, 5th edition, page no: 389', 'role': 'assistant'}]