Cobalamin or Vitamin B₁₂  is also known as the Extrinsic Factor of Castle (EF) & Anti-Pernicious Anemia Factor.

Free Online Lectures of Biochemistry for Medical, Dental and Allied Health Sciences by Biochemistry Club

Chemistry and Structure

• Vitamin B₁₂ is water soluble, heat stable and red in color.
• It contains 4.35% cobalt by weight.
• It contains one cobalt atom. Four pyrrole rings coordinated with a cobalt atom is called a Corrin ring that is very similar to the Porphyrin ring.
• The 5^th valency of the cobalt is covalently linked to a substituted benzimidazole ring. This is then called cobalamin.
• The 6^th valency of the cobalt is satisfied by any of the following groups:

1. Cyanide – when cyanide is added to R, Cyanocobalamin
2. Hydroxyl – when hydoxyl group is added to R, it is Hydroxycobalamin
3. Adenosyl – when it is taken up by the cells deoxy-adenosyl cobalamin is formed
4. Methyl group when methyl group replaces adenosyl group then methyl cobalamin is formed.

1. Cyanocobalamin

• When cyanide is added at the R position, the molecule is called cyanocobalamin.
• During the isolation procedure, cyanide is added to get stable crystals.
• The CN group has no physiological function, it is only a laboratory artefact.
• Oral preparations are in this form.

2. Hydoxycobalamin

• When hydroxyl group is attached at the R position, it is called hydroxy cobalamin or vitamin B12a.
• Injectable preparations are in this form.

3. Adenosylcobalamin (Ado-B12)

• When taken up by the cells, the above groups are removed and deoxy adenosyl cobalamin or Ado-B12 is formed.
• This is the major storage form, seen in liver.

4. Methylcobalamin (Methyl B12)

• When the methyl group replaces adenosyl group, it is known as …

All these lectures are organized and listed in detail in their proper sections. To view these lessons please visit the Vitamins Section. This can be approached by directly clicking the Biochemistry I button or it can also be approached from the drop down menu in Biochemistry I tab. Once you reach the section click the curriculum tab to view the full list in the section.

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