Figure 1.

One Carbon Metabolism Metabolic Pathways. Folate cycle metabolites and enzymes (green boxes): 5,10-CH₂-THF, 5,10-methylenetetrahydrofolate; 5,10-CH=THF, 5,10-methenyl-tetrahydrofolate; 10fTHF, 10-formyl-tetrahydrofolate; 5mTHF, 5-methyl-tetrahydrofolate; DHF, dihydrofolate; Gly, glycine; Ser, serine; dTMP, thymidine monophosphate; dUMP, deoxyuridine monophosphate; DHFR, dihydrofolate reductase; MTHFD1/2, methylenetetrahydrofolate dehydrogenase; MTHFR, 5,10-methylenetetrahydrofolate reductase; SHMT1, serine hydroxymethyltransferase 1; TYMS, thymidylate synthase. Methionine cycle metabolites and enzymes (red boxes): DMG, dimethylglycine; Hcy, homocysteine; Met, methionine; SAH, S-adenosylhomocysteine; SAM, S-adenosylmethionine, Sar, sarcosine; AHCY; S-adenosyl-L-homocysteine hydrolase; BHMT, betaine-homocysteine S-methyltransferase; CHDH, choline dehydrogenase; GNMT, glycine N-methyltransferase; MATI/III, methionine adenosyltransferase; MTR, methionine synthase; MTRR, methionine synthase reductase. Transsulfuration pathway metabolites and enzymes (orange boxes): Cth, cystathionine; Cys, cysteine; Hse, homoserine; CBS, cystathionine β-synthase; CTH, cystathionine γ-lyase. Key methyltransferase enzymes (blue box): DNMTs, de novo and maintenance DNA methyltransferases; HMT, histone methyltransferase; PRMT, protein arginine methyltransferase; PEMT, phosphatidylethanolamine N-methyltransferase. Choline metabolites and enzymes (purple boxes): CDP-choline, cytidine diphosphate-choline; PC, phosphatidylcholine; pCholine, phosphocholine; PE, phosphatidylethanolamine; CCT, CTP:phosphocholine cytidylyltransferase; ChAT, choline acetyltransferase; CK, choline kinase; CPT, cholinephosphotransferase; PLD, phospholipase D. Coenzymes (grey circles): vitamin B₂, B₆ and B₁₂. *enzymes mainly expressed in the liver; ^# BHMT1 is also expressed in the kidney.