Function

n humans, vitamin C is a highly effective antioxidant, acting to lessen oxidative stress, a substrate for ascorbate peroxidase,[4] as well as an enzyme cofactor for the biosynthesis of many important biochemicals. Vitamin C acts as an electron donor for eight different enzymes:[9]

* Three participate in collagen hydroxylation.[10][11][12] These reactions add hydroxyl groups to the amino acids proline or lysine in the collagen molecule (via prolyl hydroxylase and lysyl hydroxylase), thereby allowing the collagen molecule to assume its triple helix structure and making vitamin C essential to the development and maintenance of scar tissue, blood vessels, and cartilage.[13]

* Two are necessary for synthesis of carnitine.[14][15] Carnitine is essential for the transport of fatty acids into mitochondria for ATP generation.

* The remaining three have the following functions:
o dopamine beta hydroxylase participates in the biosynthesis of norepinephrine from dopamine.[16][17]
o another enzyme adds amide groups to peptide hormones, greatly increasing their stability.[18][19]
o one modulates tyrosine metabolism.[20][21]

Biological tissues that accumulate over 100 times the level in blood plasma of vitamin C are the adrenal glands, pituitary, thymus, corpus luteum, and retina.[22] Those with 10 to 50 times the concentration present in blood plasma include the brain, spleen, lung, testicle, lymph nodes, liver, thyroid, small intestinal mucosa, leukocytes, pancreas, kidney and salivary glands