Pathway · 4 proteins
Riboflavin metabolism
Proteins of this group that KEGG places on its “Riboflavin metabolism” map for Aquifex aeolicus.
How it works
This map shows how riboflavin (vitamin B2) is built from GTP and a five-carbon sugar phosphate and then turned into FMN and FAD. The proteins here build the lumazine ring and the ribityl side chain. A related enzyme makes the modified flavin used by some decarboxylases.
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 |
|---|---|---|---|---|---|
| 6,7-dimethyl-8-ribityllumazine synthase | 2.5.1.78 | (2S)-2-hydroxy-3-oxobutyl phosphate + 5-amino-6-(D-ribitylamino)uracil = 6,7-dimethyl-8-(1-D-ribityl)lumazine + phosphate + 2 H2O + H(+) | — | 154 | Step named |
| Riboflavin biosynthesis protein RibD | 1.1.1.193; 3.5.4.26 | 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)-pyrimidine + H2O + H(+) = 5-amino-6-(5-phospho-D-ribosylamino)uracil + NH4(+) | Zn(2+) | 356 | Step named |
| 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone 5'-phosphate reductase | 1.1.1.302 | 2,5-diamino-6-(1-D-ribitylamino)pyrimidin-4(3H)-one 5'-phosphate + NADP(+) = 2,5-diamino-6-(1-D-ribosylamino)pyrimidin-4(3H)-one 5'-phosphate + NADPH + H(+) | — | 224 | Step named |
| Flavin prenyltransferase UbiX | 2.5.1.129 | dimethylallyl phosphate + FMNH2 = prenylated FMNH2 + phosphate | FMN | 189 | 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 |
|---|---|---|---|---|---|
| Riboflavin biosynthesis proteinHome: NAD and flavins | 2.7.1.26; 2.7.7.2 | FMN + ATP + H(+) = FAD + diphosphate | — | 314 | Step named |
| Riboflavin synthaseHome: NAD and flavins | 2.5.1.9 | 2 6,7-dimethyl-8-(1-D-ribityl)lumazine + H(+) = 5-amino-6-(D-ribitylamino)uracil + riboflavin | — | 207 | Step named |
| Riboflavin biosynthesis protein RibBAHome: Folate biosynthesis | 3.5.4.25; 4.1.99.12 | D-ribulose 5-phosphate = (2S)-2-hydroxy-3-oxobutyl phosphate + formate + H(+) | D-ribulose 5-phosphate, Mg(2+), Zn(2+) | 406 | Step named |
Origins
Could riboflavin (vitamin B2) and its active forms FMN and FAD have been available before cells?
A self-capping ribozyme (Huang and Yarus) attaches FMN to its own end when supplied with it. The books searched describe no prebiotic route to riboflavin itself.
Riboflavin is built from a purine nucleotide and a sugar phosphate in several steps, and in many bacteria an RNA switch that binds FMN controls the genes that make it. Four proteins of the minimal set serve this pathway.
From the books: Ribas de Pouplana (ed.), The Genetic Code and the Origin of Life, p. 67; 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 aae00740 (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 · Nicotinate and nicotinamide metabolism · Biotin metabolism · Cysteine and methionine metabolism · Porphyrin metabolism · Pyruvate metabolism · Not yet placed in a pathway