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Vitamin C (L-ascorbate)

Vitamin C is an essential nutrient for higher primates, and a small number of other species. The presence of ascorbate is required for a range of essential metabolic reactions in all animals and in plants and is made internally by almost all organisms. It is widely known as the vitamin that prevents scurvy in humans.

The pharmacophore of vitamin C is the ascorbate ion. In living organisms, ascorbate is an antioxidant, as it protects the body against oxidative stress,and a cofactor in several vital enzymatic reactions.

As a nutrient, its uses and the daily requirement are matters of on-going debate. As a food additive, vitamin C is used as an antioxidant preservative and an acidity regulator.
Several E numbers account for the vitamin, depending on its chemical structure: E300 as ascorbic acid, E301 as sodium ascorbate, E302 as calcium ascorbate, and E303 as potassium ascorbate.

In humans, vitamin C is a highly effective antioxidant, acting to lessen oxidative stress, a substrate for ascorbate peroxidase, as well as an enzyme cofactor for the biosynthesis of many important biochemicals.

Vitamin C acts as an electron donor for eight different enzymes. Of the eight enzymes, three participate in collagen hydroxylation. These reactions add hydroxyl groups to the amino acids proline or lysine in the collagen molecule, thereby allowing the collagen molecule to assume its triple helix structure. Two other vitamin C dependent enzymes are necessary for synthesis of carnitine. Carnitine is essential for the transport of fatty acids into mitochondria for ATP generation. The remaining three vitamin C dependent enzymes have the following functions: one participates in the biosynthesis of norepinephrine from dopamine, one adds amide groups to peptide hormones, greatly increasing their stability, and one modulates tyrosine metabolism.

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. 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.

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