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. 2021 Dec 23;58(1):16. doi: 10.3390/medicina58010016

Figure 2.

Figure 2

Compartmentalization of FOCM. Note the presence of the folate-methionine one carbon cycle metabolism in the cytoplasm (cytosol), mitochondria and nucleus. Additionally, note the importance of formate being transferred from the mitochondria to the nucleus, as well as S-adenosylmethionine (SAM) via nuclear pores. Importantly, deoxythymidine monophosphate (dTMP) synthesis occurs in the cytosol, nucleus and mitochondria, whereas purine synthesis and methionine synthesis take place within the cytosol. Mitochondrial FOCM generates formate for cytosolic and nuclear FOCM and biosynthetic precursors for mtDNA synthesis and mitochondrial protein translation. Thymidylate synthase (TYMS) converts deoxyuridine monophosphate (dUMP) to dTMP in a 5,10-methylene-THF-dependent reaction (not shown). It is important to note that mitochondrial SAM (Mt SAM) is derived from cytosolic SAM (cSAM). Additionally, the Krebs cycle also resides within the mitochondria and provides NADH and FADH2 to the electron transport chain for ATP production. ATP = adenosine triphosphate; c = cytosol; ETC = electron transport chain; FAD = flavin adenine dinucleotide; FADH = reduced flavin adenine dinucleotide; FFA = free fatty acids; HHcy = hyperhomocysteinemia; MS = methionine synthase; Mt = mitochondria; NADH = reduced nicotinamide adenine dinucleotide; T = thymidylate-thymine; U = uracil.