Pathway · 3 proteins
Cysteine and methionine metabolism
Proteins of this group that KEGG places on its “Cysteine and methionine metabolism” map for Aquifex aeolicus.
How it works
This map covers the sulfur amino acids and S-adenosylmethionine (SAM), the cell's main methyl donor. The proteins here make methionine and SAM and recycle the by-products of SAM use, through the methionine salvage route, back into methionine. They also make decarboxylated SAM for building polyamines.
Grouped by KEGG pathway map. The explanation above is the atlas’s own; the map itself covers more organisms than Aquifex.
Its proteins
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| S-adenosylmethionine synthase | 2.5.1.6 | L-methionine + ATP + H2O = S-adenosyl-L-methionine + phosphate + diphosphate | Mg(2+), K(+) | 376 | Step named |
| 5-methyltetrahydropteroyltriglutamate--homocysteine methyltransferase | 2.1.1.14 | 5-methyltetrahydropteroyltri-L-glutamate + L-homocysteine = tetrahydropteroyltri-L-glutamate + L-methionine | Zn(2+) | 761 | Step named |
| Probable aspartate/prephenate aminotransferase | 2.6.1.1; 2.6.1.78 | L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate | — | 394 | Step named |
Origins
How could the sulfur amino acids, and the methyl donor S-adenosylmethionine, have been supplied before cells?
The books searched say little about prebiotic routes to cysteine or methionine. RNA can bind S-adenosylmethionine with great specificity, which is cited as one thing RNA can do on its own.
In many bacteria an RNA switch binds S-adenosylmethionine and turns off the genes needed to make more of it. Each such riboswitch binds only one molecule, and more than a dozen kinds are known.
From the books: Atkins, Gesteland & Cech (eds.), RNA Worlds, p. 7; Nelson & Cox, Lehninger Principles of Biochemistry, p. 1134.
The wider question for this part of the cell: origins for manufacturing cofactors and vitamins.
Sources
- KEGG map aae00270 (enzymes of this organism highlighted)
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 · Serine, glycine and sulfur · Folate biosynthesis · Oxidative phosphorylation · Thiamine metabolism · Pantothenate and CoA biosynthesis · Glycine, serine and threonine metabolism · Riboflavin metabolism · Nicotinate and nicotinamide metabolism · Biotin metabolism · Porphyrin metabolism · Pyruvate metabolism · Not yet placed in a pathway