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Case details

A 4 -year-old boy was brought for consultation for hematuria, edema of lower extremities as well as swollen right leg. He was the 12th born in a poor family, where one previous child died from malnutrition and dehydration in the period of infancy. The child was fed only with cow’s milk and biscuits. From the period of five months, the boy manifested irritability, sweating, poor appetite and cried when somebody touched him

At admission the baby was afebrile, pale, and malnourished. Clinical evaluation showed no organomegaly, no neurological signs, gingival bleeding was there and only one tooth was present. The child was diagnosed with ‘Scurvy’, which is a clinical sate of severe vitamin C deficiency. Vitamin C has an important role in the body, besides performing multiple functions, and acting as an antioxidant, it is also required as a coenzyme for specific reactions.

Which ‘one’ of the following conversions is inhibited in scurvy?

A. Conversion of Pyruvate to Acetyl co A

B. Conversion of Propionyl co A to succinyl co A

C. Conversion of Homocysteine to Methionine

D. Conversion of Proline to Hydroxyproline

E. Conversion of Succinate to fumarate.

The correct answer is D- Conversion of Proline to Hydroxyproline.

Basic concept

Vitamin C dependent Proline and lysine hydroxylases are required for the postsynthetic modification of procollagen to collagen. The proline to hydroxyproline conversion reaction can be represented as follows:

 Hydroxylation of Proline

Figure- Hydroxylation of proline is an essential prerequisite for collagen synthesis. The hydroxylation of Lysine is also carried out in the same manner.

Deficiency of vitamin C leads to impaired collagen synthesis, causing capillary fragility, poor wound healing, and bony abnormalities in affected adults and children.

The functions of vitamin C can be summarized alphabetically as follows:

A) It is an antioxidant and is also required for the amino acid metabolism such as metabolism of tryptophan and tyrosine.

B) Vitamin C is required for Bone formation, Bile acid synthesis and Brain function

C) It is required for the synthesis of Collagen, Carnitine, Complement and Catecholamines.

D) Drug detoxification- It is a component of many drug-metabolizing enzyme systems, particularly the mixed-function oxidase systems.

E) Enzymes– Vitamin C is the coenzyme for two groups of hydroxylases. These are copper-containing hydroxylases and the α-ketoglutarate-linked iron-containing hydroxylases. 

F) Folic acid metabolism- Ascorbic acid is required for reducing Folic acid to its tetrahydrofolate form. Thus it helps in the maturation of red blood cells.

G) General body growth- Vitamin C has a protective role and because of its role in disease prevention, it stimulates general body growth.

H) Vitamin C is helpful in the reconversion of met haemoglobin to haemoglobin. Vitamin C is also a cofactor in the synthesis of peptide hormones, corticosteroids, and aldosterone.

I) The vitamin C has an important role in the absorption and conversion of Iron to its storage form. This may contribute to the anemia seen with vitamin C deficiency.

Vitamin C promotes Immunity and has been proposed to have pharmacological benefits in preventing cancer, infections, and the common cold.

As regards other options

A. Conversion of Pyruvate to Acetyl co A- requires Thiamine (TPP), Pantothenic acid (CoASH), Lipoic acid, FAD and NAD + as coenzymes. The reaction is catalyzed by Pyruvate dehydrogenase complex, which is a multienzyme complex.

B. Conversion of Propionyl co A to succinyl co A is a multistep process. Biotin and vitamin B12 are required for the metabolism of Propionyl co A.

C. Conversion of Homocysteine to Methionine- requires the presence of Methylcobalamine and folic acid, the reaction is catalyzed by Methionine synthase.

E. Conversion of Succinate to fumarate- is catalyzed by succinate dehydrogenase; the enzyme requires the presence of FAD (Riboflavin) for its action.

Thus in vitamin C deficiency, the conversion of proline to hydroxyproline is inhibited.

For further reading

Check the following links

Functions of Vitamin C

http://www.namrata.co/a-to-i-of-vitamin-c-functions-of-vitamin-c-simplified/

Vitamin C deficiency

http://www.slideshare.net/namarta28/vitamin-c-deficiency

 

 

 

 

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