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Folate Derivatives in Human Cells: Studies on Normal and 5,10-Methylenetetrahydrofolate Reductase-Deficient Fibroblasts¹

Department of Biochemistry, School of Hygiene and Public Health, The Johns Hopkins University, 615 North Wolfe Street, Baltimore, MD 21205

The distribution of folylpolyglutamates in normal and methylenetetrahydrofolate reductase-deficient human fibroblasts cultured in medium containing folic acid or 5-methyltetrahydrofolic acid has been determined. Human fibroblasts concentrated these folates to higher levels than in the medium, an effect that was more pronounced with methyltetrahydrofolate as the folate source. Over 95% of the intracellular vitamin derivatives were polyglutamates of chain length 2 to 10. The major derivatives were hexaglutamates in cells cultured with folic acid and heptaglutamates in cells cultured with methyltetrahydrofolic acid. No significant differences were detected in the polyglutamate distribution between normal and methylenetetrahydrofolate reductase-deficient fibroblasts. Excess medium methionine reduced cell growth rates and intracellular vitamin levels and changed the predominant polyglutamate in cells cultured with methyltetrahydrofolate from hepta- to hexaglutamate. No significant differences were seen between the overall folate polyglutamate distributions of different one-carbon folate pools of normal human fibroblasts, although slight changes in the proportions of individual polyglutamate forms were detected in the different pools.

KEY WORDS: • human cells • fibroblasts • folylpolyglutamates • folate distribution • methylenetetrahydrofolate reductase deficiency

¹ Supported in part by grant CA 22717 from the National Cancer Institute, Department of Health and Human Services.

² To whom reprint requests should be addressed.

Manuscript received 18 March 1982.