Fig. 2.

Vitamin B₁₂ depletion or MTR disruption results in elevated 5-methylTHF in cells (A and B) and nuclei (C). (A) Distribution of folate one-carbon forms in human fibroblasts. The percentages of folate forms are shown for one cell line of each cblG (WG4215, white bars) and control (MCH058, gray bars). (B and C) Nitrous oxide-induced changes in folate one-carbon distribution in HeLa cells (B) and nuclei (C). The percentages of folate forms present in HeLa cells and nuclei maintained in vitamin B₁₂-depleted (white bars) or -replete (gray bars) conditions are shown. All measurements were made in duplicate. Data are shown as mean ± SD. Differences in folate forms between replete and depleted conditions were determined by a Student’s two-tailed t test. For C, a Western blot confirmed that nuclei were free of cytoplasmic contamination (SI Appendix, Fig. S1). In A–C, statistical significance is denoted as follows: NS, not significant (P > 0.05); *P = 0.01 < P < 0.05; **P = 0.01 < P < 0.001; ***P < 0.001.