5-Methyltetrahydrofolate: synthesis and utilization in normal and SV40-transformed BHK-21 cells

Abstract

BHK-21 cells and SV40-transformed BHK-21 cells (A-8) grew rapidly in a medium containing methionine (I). BHK-21 cells also proliferated in a methionine-deficient medium (II) supplemented with homocysteine and vitamin B₁₂; however, the A-8 cells did not proliferate and ultimately died in this medium. The 5,10-methylenetetrahydrofolate reductase activity in transformed cells was only 10% of that found in BHK-21 cells. While A-8 cells in medium II could not be maintained on folate or 5-formyltetrahydrofolate, they survived and even proliferated slowly when provided 5-methyltetrahdyrofolate. The low level of the reductase in A-8 cells and the inability of these cells to utilize folate or 5-formyltetrahydrofolate suggests that A-8 cells are unable to synthesize 5-methyltetrahydrofolate at a rate that will satisfy the cellular demands for methionine.