If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
Synonyms: vitamin B6 biosynthesis
|Superclasses:||Biosynthesis → Cofactors, Prosthetic Groups, Electron Carriers Biosynthesis → Vitamins Biosynthesis → Vitamin B6 Biosynthesis|
Pathway Summary from MetaCyc:
Vitamin B6 is a group term for pyridoxal (PL), pyridoxine (PN), pyridoxamine (PM) and their 5'-phosphorylated derivatives pyridoxal 5'-phosphate (PLP), pyridoxine 5'-phosphate (PNP) and pyridoxamine 5'-phosphate (PMP), which are also referred to as vitamers. Pyridoxal 5'-phosphate (PLP) is the biochemically active form, and is an essential cofactor in all living systems [John95]. It plays an important role in amino acid and carbohydrate metabolism and has recently been implicated in singlet oxygen resistance [Daub00]. Most bacteria, archaebacteria, fungi, and plants synthesize PLP in a single reaction, as described in pyridoxal 5'-phosphate biosynthesis II, although some bacteria, such as Escherichia coli, use a longer, more complex pathway (pyridoxal 5'-phosphate biosynthesis I) [Yang98b, Sivaraman03]. Animals do not synthesize this compound, making it an essential nutrient in their diet.
PLP is an essential cofactor of numerous metabolic enzymes, predominantly in amino acid metabolism. It is one of the most versatile cofactors and participates in transamination, decarboxylation, racemization, Cα-Cβ cleavage and α-β elimination reactions. In humans this vitamin has a role in numerous functions ranging from modulation of hormone function to potent antioxidant activity.
About This Pathway
The biosynthesis of this vitamin was thoroughly studied in Escherichia coli and involves two branches with seven enzymatic steps. In one branch, the sequential action of the enzymes Epd, PdxB and SerC results in the convesrion of erythrose 4-phosphate into 4-phosphohydroxy-L-threonine. The latter then undergoes oxidation and decarboxylation by PdxA to form 3-hydroxy-1-aminoacetone phosphate. In the other branch, deoxyxylulose 5-phosphate (DXP) is derived from glyceraldehyde 3-phosphate (GAP) and pyruvate by the action of Dxs. The products of the two branches, i.e. 3-hydroxy-1-aminoacetone phosphate and DXP, are then condensed by PdxJ to form PNP, which enters the salvage pathway to undergo oxidation by PdxH to form the PLP cofactor.
From the six pdx genes, two of them, epd and serC, are involved in other metabolic processes, but pdxA, pdxB, pdxJ and pdxH are unique for PLP biosynthesis [Lam92a]. PdxJ, the PNP synthase is the key ezyme that catalyzes a multistep ring closure yielding PNP and inorganic phosphate (Pi). This is the last step in the de novo synthetic pathway.
An alternative DXP-independent pathway for PNP biosynthesis is described at pyridoxal 5'-phosphate biosynthesis II.
Variants: pyridoxal 5'-phosphate salvage I
Pathway Evidence Glyph:
Key to pathway glyph edge colors:
An enzyme catalyzing this reaction is present in this organism
No enzyme catalyzing this reaction has been identified in this organism
The reaction and any enzyme that catalyzes it (if one has been identified) is unique to this pathway
Represents spontaneous reactions, or lines that do not represent reactions (e.g. in polymerization pathways)
Fitzpatrick07: Fitzpatrick TB, Amrhein N, Kappes B, Macheroux P, Tews I, Raschle T (2007). "Two independent routes of de novo vitamin B6 biosynthesis: not that different after all." Biochem J 407(1);1-13. PMID: 17822383
Lam92a: Lam HM, Tancula E, Dempsey WB, Winkler ME (1992). "Suppression of insertions in the complex pdxJ operon of Escherichia coli K-12 by lon and other mutations." J Bacteriol 1992;174(5);1554-67. PMID: 1537800
Sivaraman03: Sivaraman J, Li Y, Banks J, Cane DE, Matte A, Cygler M (2003). "Crystal structure of Escherichia coli PdxA, an enzyme involved in the pyridoxal phosphate biosynthesis pathway." J Biol Chem 278(44);43682-90. PMID: 12896974
Yang98b: Yang Y, Zhao G, Man TK, Winkler ME (1998). "Involvement of the gapA- and epd (gapB)-encoded dehydrogenases in pyridoxal 5'-phosphate coenzyme biosynthesis in Escherichia coli K-12." J Bacteriol 1998;180(16);4294-9. PMID: 9696782
Herz00: Herz S, Wungsintaweekul J, Schuhr CA, Hecht S, Luttgen H, Sagner S, Fellermeier M, Eisenreich W, Zenk MH, Bacher A, Rohdich F (2000). "Biosynthesis of terpenoids: YgbB protein converts 4-diphosphocytidyl-2C-methyl-D-erythritol 2-phosphate to 2C-methyl-D-erythritol 2,4-cyclodiphosphate." Proc Natl Acad Sci U S A 97(6);2486-90. PMID: 10694574
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