Pathway · 1 proteins
Serine, glycine and sulfur
One-carbon and sulfur chemistry links these amino-acid pools.
How it works
- Serine metabolism connects amino-acid synthesis to carbon intermediates and one-carbon chemistry.
- Serine hydroxymethyltransferase can interconvert serine and glycine while transferring a one-carbon unit to or from tetrahydrofolate.
- Cysteine synthesis connects an organic carbon skeleton to usable sulfur. Its enzymes and sulfur source differ among routes; the selected organism’s pathway is described in the system evidence.
Grouped by the atlas’s curated pathway map. The table order is not a proven reaction order.
Its proteins
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Cysteine synthase | 2.5.1.47 | O-acetyl-L-serine + hydrogen sulfide = L-cysteine + acetate | — | 327 | Step named |
Also part of this pathway
These proteins are described under another pathway, but also take part here.
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Probable glycine dehydrogenase (decarboxylating) subunit 1Home: Folate-linked carbon transfer | 1.4.4.2 | N(6)-[(R)-lipoyl]-L-lysyl-[glycine-cleavage complex H protein] + glycine + H(+) = N(6)-[(R)-S(8)-aminomethyldihydrolipoyl]-L-lysyl-[glycine-cleavage complex H protein] + CO2 | — | 439 | Step named |
| Probable glycine dehydrogenase (decarboxylating) subunit 2Home: Folate-linked carbon transfer | 1.4.4.2 | N(6)-[(R)-lipoyl]-L-lysyl-[glycine-cleavage complex H protein] + glycine + H(+) = N(6)-[(R)-S(8)-aminomethyldihydrolipoyl]-L-lysyl-[glycine-cleavage complex H protein] + CO2 | — | 482 | Step named |
| Serine hydroxymethyltransferaseHome: Amino-acid connections | 2.1.2.1 | (6R)-5,10-methylene-5,6,7,8-tetrahydrofolate + glycine + H2O = (6S)-5,6,7,8-tetrahydrofolate + L-serine | — | 428 | Step named |
| D-3-phosphoglycerate dehydrogenaseHome: Not yet placed in a pathway | 1.1.1.95 | (2R)-3-phosphoglycerate + NAD(+) = 3-phosphooxypyruvate + NADH + H(+) | — | 533 | Step named |
Origins
How could sulfur have entered amino acids before cells?
Before oxygen appeared in the atmosphere, most sulfur was probably present in reduced form, which can be added to make cysteine directly.
Cells make cysteine by first attaching an acetyl group to serine and then swapping it for sulfur, using two enzymes. Today most sulfur exists as sulfate, which must be reduced by eight electrons before it can be used.
From the books: Zubay, Origins of Life on Earth and in the Cosmos, p. 287.
The wider question for this part of the cell: origins for manufacturing cofactors and vitamins.
Sources
- Atlas pathway grouping from the VF5 reference-genome system map (Deckert et al. 1998; Braakman & Smith 2014)
Other pathways in this group: Heme and quinones · Biotin and lipoate · NAD and flavins · Thiamine and pyridoxal · Folate and pterin chemistry · Lipid and cofactor connections · Coenzyme A · Aspartate-family branches · Amino-acid connections · Folate-linked carbon transfer · Folate biosynthesis · Oxidative phosphorylation · Thiamine metabolism · Pantothenate and CoA biosynthesis · Glycine, serine and threonine metabolism · Riboflavin metabolism · Nicotinate and nicotinamide metabolism · Biotin metabolism · Cysteine and methionine metabolism · Porphyrin metabolism · Pyruvate metabolism · Not yet placed in a pathway