Vitamin B12 (Methylcobalamin)

Methylcobalamin is the active coenzyme form of vitamin B12 required for two enzymes: methionine synthase (converting homocysteine to methionine, essential for the methylation cycle and SAM production) and methylmalonyl-CoA mutase (converting methylmalonyl-CoA to succinyl-CoA for citric acid cycle entry). Deficiency impairs myelin sheath synthesis, raises neurotoxic homocysteine, and causes megaloblastic anaemia. Injectable methylcobalamin achieves high plasma levels without dependence on intrinsic factor (a cofactor for gut absorption).