Vitamin C (ascorbic acid) is a water-soluble vitamin found in food and used as a dietary supplement. This vitamin plays key roles as a cofactor for hydroxylase enzymes, notably doapmine beta-hydroxylase and those involved in collagen synthesis. For the former, vitamin C helps facilitate the conversion of dopamine to norepinephrine. For the latter, vitamin C is involved in the hydroxylation of proline and lysine residues. It also plays an important role in the reduction of iron (III) to iron (II), which is required for GI absorption of iron. This property also makes vitamin C useful as an ancillary treatment for methemolobinemia.