Bone marrow cells from patients with vitamin B12 deficiency took up much less N5-methyltetrahydrofolate(MeTHF) than did normal bone marrow cells but showed no significant reduction in pterolyglutamate (PGA) uptake. Addition of B12 to the incubation medium enhanced the cell uptake of MeTHF only in B12-deficient patients. These data support the concept of a B12 requirement for cell uptake of MeTHF.

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