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. Author manuscript; available in PMC: 2022 Jul 15.
Published in final edited form as: Nat Metab. 2021 Nov 18;3(11):1512–1520. doi: 10.1038/s42255-021-00465-w

Figure 1. MTR is a minor source of methionine in cell lines, tissues and tumors.

Figure 1.

(A) Schematic showing the activity of MTR at the intersection of the folate and methionine cycles. MTR = methionine synthase, MTHFR = methylenetetrahydrofolate reductase, BHMT = betaine-homocysteine S-methyltransferase, SHMT = serine hydroxymethyltransferase. (B) Relative protein levels of MTR and BHMT in mice from [24]. (C) Methionine labeling in cell lines after culturing for 4 h in media containing [U-13C]methionine (mean ± SD, n = 6 for HCT116 cells, n = 3 for 293T and HepG2). (D) Methionine M+4 fraction from 4 h [U-13C]methionine tracing in HCT116 cultured in media containing indicated methionine and folate concentrations (mean ± SD, n = 6 for 9 μM folic acid and 200 μM methionine, n = 3 for others). (E) Methionine (left) and S-adenosyl-methionine (SAM, right) labeling of PDAC tumors and normal tissues, and methionine labeling of serum in male C57BL/6 mice after [U-13C]methionine infusion for 2.5 h (mean ± SD, n = 3 mice for methionine labeling and n = 2 mice for SAM labeling; two technical replicates were included for each tumor). (F) Betaine labeling (M+6) in serum (left), and methionine and SAM labeling (M+1, right) in tissues of male C57BL/6 mice after [13C5,15N]betaine infusion for 4 h (mean ± SD, n = 3 mice).