In vitamin B12 deficiency, folate is trapped in the form of
Formyl THFA
Methenyl THFA
Methyl-THFA
Methylene-THFA
Methylation of homocysteine to methionine is the only way of regeneration of active THFA from methyl THFA. Methionine synthase reaction requires methyl cobalamin. So, deficiency of methyl-B12 leads to trapping of THFA in less utilised methyl-THFA - phenomenon known as folate trap.
Vitamins and Minerals