Ascorbic Acid (Vitamin C)

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Chapter: Biochemistry : Vitamins

The active form of vitamin C is ascorbic acid .


The active form of vitamin C is ascorbic acid (Figure 28.8). The main function of ascorbate is as a reducing agent in several different reactions. Vitamin C has a well-documented role as a coenzyme in hydroxylation reactions (for example, hydroxylation of prolyl and lysyl residues of collagen;). Vitamin C is, therefore, required for the maintenance of normal connective tissue as well as for wound healing. Vitamin C also reduces ferric iron to the ferrous form, thereby facilitating the absorption of dietary iron from the intestine.

Figure 28.8 Structure of ascorbic acid.


A. Deficiency of ascorbic acid

A deficiency of ascorbic acid results in scurvy, a disease characterized by sore and spongy gums, loose teeth, fragile blood vessels, swollen joints, fatigue, and a microcytic anemia caused by decreased absorption of iron (Figure 28.9). Many of the deficiency symptoms can be explained by a deficiency in the hydroxylation of collagen, resulting in defective connective tissue.

Figure 28.9 Structures of vitamin B6 and the antituberculosis drug isoniazid.


B. Prevention of chronic disease

Vitamin C is one of a group of nutrients that includes vitamin E and β-carotene, which are known as antioxidants. [Note: Ascorbate regenerates the functional, reduced form of vitamin E.] Consumption of diets rich in these compounds is associated with a decreased incidence of some chronic diseases, such as coronary heart disease and certain cancers. However, clinical trials involving supplementation with the isolated antioxidants have failed to demonstrate any convincing beneficial effects.

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