Pathway · 2 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 |
|---|---|---|---|---|---|
| Peptidoglycan editing factor PgeF | 3.5.-.- | — | Zn(2+), Cu(2+) | 206 | Step named |
| S-adenosylmethionine decarboxylase proenzyme | 4.1.1.50 | S-adenosyl-L-methionine + H(+) = S-adenosyl 3-(methylsulfanyl)propylamine + CO2 | — | 135 | 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 |
|---|---|---|---|---|---|
| Malate dehydrogenase 1Home: Reductive TCA machinery | 1.1.1.37 | (S)-malate + NAD(+) = oxaloacetate + NADH + H(+) | — | 335 | Step named |
| AspartokinaseHome: Aspartate-family branches | 2.7.2.4 | L-aspartate + ATP = 4-phospho-L-aspartate + ADP | — | 415 | Step named |
| AdenosylhomocysteinaseHome: Cysteine and methionine metabolism | 3.13.2.1 | S-adenosyl-L-homocysteine + H2O = L-homocysteine + adenosine | — | 418 | Step named |
| Homoserine kinaseHome: Aspartate-family branches | 2.7.1.39 | L-homoserine + ATP = O-phospho-L-homoserine + ADP + H(+) | — | 297 | Step named |
| Homoserine dehydrogenaseHome: Aspartate-family branches | 1.1.1.3 | L-homoserine + NADP(+) = L-aspartate 4-semialdehyde + NADPH + H(+) | — | 435 | Step named |
| Aspartate-semialdehyde dehydrogenaseHome: Aspartate-family branches | 1.2.1.11 | L-aspartate 4-semialdehyde + phosphate + NADP(+) = 4-phospho-L-aspartate + NADPH + H(+) | — | 340 | Step named |
| Acireductone dioxygenaseHome: Cysteine and methionine metabolism | 1.13.11.53; 1.13.11.54 | 1,2-dihydroxy-5-(methylsulfanyl)pent-1-en-3-one + O2 = 3-(methylsulfanyl)propanoate + CO + formate + 2 H(+) | Fe(2+), Ni(2+) | 183 | Step named |
| Enolase-phosphatase E1Home: Cysteine and methionine metabolism | 3.1.3.77 | 5-methylsulfanyl-2,3-dioxopentyl phosphate + H2O = 1,2-dihydroxy-5-(methylsulfanyl)pent-1-en-3-one + phosphate | Mg(2+) | 223 | Step named |
| Methylthioribulose-1-phosphate dehydrataseHome: Cysteine and methionine metabolism | 4.2.1.109 | 5-(methylsulfanyl)-D-ribulose 1-phosphate = 5-methylsulfanyl-2,3-dioxopentyl phosphate + H2O | Zn(2+) | 208 | Step named |
| Methylthioribose-1-phosphate isomeraseHome: Cysteine and methionine metabolism | 5.3.1.23 | 5-(methylsulfanyl)-alpha-D-ribose 1-phosphate = 5-(methylsulfanyl)-D-ribulose 1-phosphate | — | 456 | Step named |
| 5-methylthioadenosine/S-adenosylhomocysteine deaminaseHome: Cysteine and methionine metabolism | 3.5.4.28; 3.5.4.31 | S-adenosyl-L-homocysteine + H2O + H(+) = S-inosyl-L-homocysteine + NH4(+) | Zn(2+) | 430 | Step named |
| Probable 6-oxopurine nucleoside phosphorylaseHome: Not yet placed in a pathway | 2.4.2.1 | a purine D-ribonucleoside + phosphate = a purine nucleobase + alpha-D-ribose 1-phosphate | — | 277 | Step named |
| S-adenosylmethionine synthaseHome: Cysteine and methionine metabolism | 2.5.1.6 | L-methionine + ATP + H2O = S-adenosyl-L-methionine + phosphate + diphosphate | Mg(2+), K(+) | 376 | Step named |
| Cysteine synthaseHome: Serine, glycine and sulfur | 2.5.1.47 | O-acetyl-L-serine + hydrogen sulfide = L-cysteine + acetate | — | 327 | Step named |
| 5-methyltetrahydropteroyltriglutamate--homocysteine methyltransferaseHome: Cysteine and methionine metabolism | 2.1.1.14 | 5-methyltetrahydropteroyltri-L-glutamate + L-homocysteine = tetrahydropteroyltri-L-glutamate + L-methionine | Zn(2+) | 761 | Step named |
| Probable branched-chain-amino-acid aminotransferaseHome: Pantothenate and CoA biosynthesis | 2.6.1.42 | L-leucine + 2-oxoglutarate = 4-methyl-2-oxopentanoate + L-glutamate | — | 311 | Step named |
| Probable aspartate/prephenate aminotransferaseHome: Cysteine and methionine metabolism | 2.6.1.1; 2.6.1.78 | L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate | — | 394 | 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 |
| Polyamine aminopropyltransferase 1Home: Not yet placed in a pathway | 2.5.1.16 | S-adenosyl 3-(methylsulfanyl)propylamine + putrescine = S-methyl-5'-thioadenosine + spermidine + H(+) | — | 280 | Unspecified |
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 copying and repairing the genome.
Sources
- KEGG map aae00270 (enzymes of this organism highlighted)
Other pathways in this group: DNA damage repair · DNA synthesis · Topology management · Joining and end processing · Recombination and restart · Chromosome preparation · Initiation and opening · Homologous recombination · Base excision repair · Not yet placed in a pathway