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Wednesday, January 09, 2008

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


2. Homocysteine methyl transferase


Lippincott 3rd Edition Page 373

Chaterjee 6th Edition Page 181





Most books


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


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


Daily requirements of Vitamin B12 in micrograms (mg)



In normal adults





1 to 2

Pregnancy and lactation



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

1 comment:

  1. This is really interesting take on the concept. I never thought of it that way. I came across this site recently which I think will be of great use . Have a look!

    DNA Methyl transferase 3B