Cobalamin

Cobalamin with the upper axial ligand noted as R

Cobalamin may refer to several chemical forms of vitamin B₁₂, depending on the upper axial ligand of the cobalt ion. These are:

• Cyanocobalamin (R = –CN)
• Hydroxocobalamin (R = –OH)
• Methylcobalamin (R = –CH₃), an active form of vitamin B₁₂
• Adenosylcobalamin (R = –Ado), also an active form of vitamin B₁₂

Cobalamin is susceptible to acid. During its biosynthesis, complexes are formed which protect it.