Vitamin C is required for ?: (A) Posttranslational modification, (B) Synthesis of epinephrine, (C) Tyrosine metabolism, (D) All of the above
Answer is D. Vitamin C (ascorbic acid) Ascorbic acid (Vitamin C) is also called antiscorbutic factor. It is very heat labile, especially in basic medium. Ascorbic acid itself is an active form. Maximum amount of vitamin C is found in adrenal coex. Ascorbic acid functions as a reducing agent and scavanger of free radicals (antioxidant). Its major functions are :- i) In collagen synthesis :- Vitamin C is required for post-translational modification by hydroxylation of proline and lysine residues conveing them into hydroxyproline and hydroxylysine. Thus vitamin C is essential for the conversion of procollagen to collagen, which is rich in hydroxyproline and hydroxylysine. Through collagen synthesis, it plays a role in formation of matrix of bone, cailage, dentine and connective tissue. ii) Synthesis of norepinephrine from dopamine by dopamine-(3-monoxygenase (dopamine-13-hydroxylase) requires Vitamin C. iii) Carnitine synthesis iv) Bile acid synthesis :- 7-a-hydroxylase requires vitamin C. v) Absorption of iron is stimulated by ascorbic acid by conversion of ferric to ferrous ions. vi) During adrenal steroid synthesis, ascorbic acid is required during hydroxylation reactions. vii) Tyrosine metabolism - Oxidation of P-hydroxy-phenylpyruvate to homogentisate. viii) Folate metabolism - Folic acid is conveed to its active form tetrahydrofolate by help of Vitamin C.