Aamir Ali KhanM.Phil BiochemistryHead of Pathology DepartmentNorthwest Institute of Health sciences Peshawar

Vitamin C or L-ascorbic acid, or simply ascorbate (the anion of ascorbic acid), is an essential nutrient for humans and certain other animal species. Vitamin C refers to a number of vitamers that have vitamin C activity in animals, including ascorbic acid and its salts, and some oxidized forms of the molecule like dehydroascorbic acid.

The name 'vitamin C' always refers to the L- enantiomer of ascorbic acid and its oxidized forms. The opposite D- enantiomer called D-ascorbate has equal antioxidant power, but is not found in nature, and has no physiological significance

Introduction

L-Ascorbic acid (vitamin C) is a white, odorless, crystalline powder.

It is freely soluble in water and relatively insoluble in organic solvents.

In a dry state, away from light, it is stable for a considerable length of time.

The appropriate daily intake of this vitamin is still in dispute. The recommended daily allowance in the United States is 60

mg (Australia and the United Kingdom recommend 30 to 40 mg; Russia recommends 100 mg).

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Sources

Vitamin C Content in foods

Ascorbic acid is involved in conversion of proline present in procollagen to hydroxyproline.This hydroxylation of proline is essential because in its absence collagen cannot form the triple helix required for the normal tissue structure

Vitamin C acts as an antioxidant and along with other antioxidant, e.g. B.carotene,vitamin E

It is present in large amounts in glandular tissue especially adrenal cortex and corpus luteum.

The reduction reaction, folic acid to tetrahydrofolic acid, needs the presence of ascorbic acid  

Functions

It takes part in the processing of certain polypeptide hormones, e.g oxytocin, ADH etc

Other reactions in which ascorbic acid is involved are the hydroxylation of dopamine to noradrenaline, synthesis of carnitine, formation of bile acids and microsomal drug metabolism

Effects of Deficiency…..Scurvy: Scurvy is likely to occur in artificially-fed infants because of low vitamin C content Breast fed infants rarely suffer from scurvy

Scurvy which is potentially fatal disease has following clinical picture, Disruption of adventitia, media, and basal laminae of blood vessels  Anemia, weakness, tendency to remain motionless Skin shows hemorrhages  At the growing ends of long bones osteoblastic function is arrested, Delayed healing of wounds and fractures.

Deficiency

So why is ascorbate so necessary to good health?Of particular interest to us here is its role in the formation of collagenCollagen is constructed of the repeating tripeptide unit

Gly–X–Y, where X and Y are generally Proline or 4- Hydroxy proline (Glycine)

The inability to hydroxylate the Proline at the Y positions when vitamin C is absent leads to collagen instability and the connective tissue problems seen in scurvy.

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