Methylcobalamin is vitamin B12 that has a methyl group (-CH3) attached to it. This typically occurs once vitamin B12 is absorbed into the cell and accepts the methyl group from methyltetrahydrofolate (the active form of folate). Once B12 is 'methylated' by folate, it transfers this single carbon methyl group to homocysteine which converts it into the amino acid, methionine. This takes place in the cytoplasm of the cell.
The Interdependence of Single Carbon Nutrients and What an Elevated Homocysteine Level Tells Us
MMA Test is More Sensitive at Diagnosing Mild or Moderate B12 Deficiency than Vitamin B12 Levels
Urinary MMA is a Superior Test For Detecting B12 Deficiency, and for Good Reason.
The MMA Test Teaches a Lot About Why B12 is So Important for Energy
First Study to Find a Link