This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nutrition & Digestion, Subject name: Biochemistry
Prolyl hydroxylase require which cofactor - 
Select and explain. 
A. Sc, B. Vitamin C, C. Mo, D. Vitamin K
B: Vitamin C
Answer: B: Vitamin C 
Explanation: Ans. is 'b' i.e., Vitamin C Hydroxvlation of proline and lvsine of collageno Hydroxylation of proline and lysine residue takes place during post-translational modification in rough ER. The enzyme catalyzing the reactions are prolyl hydroxylase (for proline) and lysyl hydroxylase (for lysine). Both these enzymes are dioxygenases using molecular oxygen (O2) and cofactor for both these enzymes is vitamin C (ascorbic acid). a-Ketoglutatrate is a coreductant, which is oxidized to succinate.Proline (or lysine) + a-ketoglutarate + O2Prolyl (or lysyl) hydroxylase-----------------------Vitamin 'C'Hydroxyproline (or hydroxylysine)+Succinateo These hydroxylated amino acids are not reprsented in the genetic code (i.e. there is no t-RNA for these), therefore they have to be synthesized post-translationally from proline and lysine residue in the polypeptides.