Vitamin B12 acts as coenzyme to Homocysteine methyl transferase

035. Vitamin B12 acts as coenzyme to which one of the following enzymes?

1. Isocitrate dehydrogenase

2. Homocysteine methyl transferase

3. Glycogen synthase

4. G-6-P dehydrogenase

Answer

2. Homocysteine methyl transferase

Reference:

Lippincott 3^rd Edition Page 373

Chaterjee 6^th Edition Page 181

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Discussion

The metabolic role of Caobamide Co-enzymes

1. Methyl malonyl CoA to Succinyl CoA conversion

2. Methylation of homocysteine to Methionine

3. Methylation of pyrimidine ring to form thymine

4. Conversion of Ribonucleotides (RNA) to Deoxyribonucleotides (DNA)

5. Metabolism of Diols (Ethylene Glycol to Acetaldehyde)

6. Intercovnersion of Glutamate and beta-methyl aspartate in bacteria

Explanation

1. Co enzyme of Isocitrate dehydrogenase is NADP

2. Co enzyme of Homocysteine methyl transferase is B₁₂

3. Glycogen synthase requires Glucose-6-P as an activation

4. Co enzyme of G-6-P dehydrogenase is NADP

Comments

Daily requirements of Vitamin B₁₂ in micrograms (mg)

Situation	mg/day
In normal adults	3
Infants	0.3
Children	1 to 2
Pregnancy and lactation	4

Tips

Nieweg’s hypothesis postulates why B12 deficiency is associated with SCID (Subacute combined degeneration of Cord) and other neurological manifestations along with with lesions of bone marrow and GIT where as Folic acid deficiency is associated only with lesions of bone marrow and GIT and little neural involvement.

It is because RNA Synthesis (for nervous system) requires folic acid where as DNA synthesis of for Bone Marrow and GIT requires both folic acid as well as B₁₂