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
Post-translational modification of hydroxylases is mediated by 
Select and explain. 
A. Vitamin K, B. Vitamin E, C. Vitamin C, D. Vitamin D
C: Vitamin C
Answer: C: Vitamin C 
Explanation: Ascorbic acid has specific roles in the copper-containing hydroxylases and the a-ketoglutarate-linked iron-containing hydroxylases. Dopamine b-hydroxylase is a copper-containing enzyme involved in the synthesis of the catecholamines (norepinephrine and epinephrine), from tyrosine in the adrenal medulla and central nervous system. During hydroxylation the Cu+ is oxidized to Cu2+; reduction back to Cu+ specifically requires ascorbate, which is oxidized to monodehydroascorbate. Reference: Harper; 30th edition; Page no: 561