Also known as Vitamin C or ascorbic acid, ascorbate serves as an antioxidant and redox factor for certain hydroxylating enzymes. Most mammals can synthesize ascorbate from glucose in the liver, but this capacity has been lost by higher primates (including humans) and guinea pigs. Thus, ascorbate is required in the diet of these animals. Its antioxidant properties derive from the high reducing potential of the carbon-carbon double bond in its five-membered lactone ring.

It undergoes one-electron oxidation to become ascorbyl radical; a further one-electron transfer yields dehydroascorbate (DHA). These oxidation steps are reversible. DHA in erythrocytes can be reduced to ascorbate by two-electron transfer from NADPH or reduced glutathione (GSH). Enzymes that require ascorbate are prolyl hydroxylase, lysyl hydroxylase and dopamine b-hydroxylase. The first two enzymes are critical in the production of collagens. Without ascorbate, collagen is insufficently hydroxylated, and this abnormal collagen accounts for the the symptoms of scurvy, such as skin lesions and blood-vessel fragility.

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