Figure 2.

The contribution of one-carbon metabolism to methylation. Serine-dependent one-carbon metabolism supports the methionine cycle and methylation reactions via two distinct pathways. Serine catabolism provides one-carbon units (C₁) and glycine, which are both required for de novo ATP synthesised via purine synthesis. ATP synthesised in this way contributes adenosine for the production of SAM from methionine. After participating in a methylation reaction, SAM becomes S-adenosylhomocysteine (SAH) and then homocysteine. Homocysteine can be re-methylated and recycled back to methionine, which requires a one-carbon unit that can also be sourced from serine catabolism to glycine.