Methionine biosynthesis in normal and transformed fibroblasts

SV-40 transformed human fibroblasts show a growth requirement for methionine, whereas normal fibroblasts do not. Activities of the N 5 -methyltetrahydrofolate-homocysteine transmethylase and N 5–10 -methylenetetrahydrofolate reductase in extracts of both cell lines are similar. These observations indicate that the absolute growth requirement for methionine observed in these transformed cells does not necessarily involve a deficiency in enzymes related to methionine synthesis.