Vitamin B12 (Cobalamin)

Vitamin B12, also known as cobalamin, is a water‑soluble, cobalt‑containing vitamin essential for human health. It functions primarily as a co‑factor for two critical enzymes—methionine synthase and methylmalonyl‑CoA mutase—supporting DNA synthesis, red-blood-cell formation, and neurological integrity.

Cobalamin is a complex organometallic compound with the molecular formula C₆₃H₈₈CoN₁₄O₁₄P. The IUPAC name is (5‑(2‑hydroxy‑5‑[3‑(1‑deoxy‑β‑D‑ribofuranosyl)‑2‑hydroxy‑4‑methoxy‑5‑methyl‑2‑pyridyl]‑5‑oxopentyl)‑cob(III)‑cobamide. Its key structural features include:
- A central cobalt ion coordinated by a corrin ring (similar to a porphyrin but with one fewer methine bridge).
- A nucleotide-like tail (5‑deoxy‑β‑D‑ribose attached to a dimethylbenzimidazole) that anchors B12 in enzymes.
- Variable axial ligands (e.g., methyl, adenosyl, hydroxyl, cyanide) that define the biologically active forms.
- The corrin ring is highly conjugated, giving B12 its deep red color and enabling redox transitions (Co(III)↔Co(II)↔Co(I) crucial for enzymatic activity).

Naturally, cobalamin is produced exclusively by microorganisms (e.g., Propionibacterium spp., Lactobacillus, Pseudomonas, and certain archaea). Commercial production uses two main approaches:
- Fermentation: Large‑scale bacterial fermentation (e.g., Pseudomonas denitrificans) yields high‑purity cyanocobalamin, the most common supplement form.
- Chemical synthesis: Complex multi‑step synthesis yields methyl‑ and adenosyl‑cobalamin, often used in “active” B12 products.
- Quality Considerations: Verification of the specific cobalamin form (cyn­ano‑ vs. methyl‑), absence of bacterial endotoxins, and stability (cobalamin is light‑ and heat‑sensitive). Good Manufacturing Practice (GMP) certified production and third-party testing (e.g., USP, NSF) are essential to ensure potency, purity, and absence of contaminants such as heavy metals or residual solvents.