If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Cofactors, Prosthetic Groups, Electron Carriers Biosynthesis → Vitamins Biosynthesis → Folate Biosynthesis|
Expected Taxonomic Range: Viridiplantae
The formation of the formyl and methyl derivatives of tetrahydrofolate (vitamin B9) directly involved in or representing sidesteps of the biosynthesis of this vital cofactors [Cossins97] [Hanson00] is displayed in this pathway. Folates are involved in a wide range of key metabolic functions in plants [Hanson02] [Jabrin03] mediating fluxes through C1-pathways with a high demand for methylated compounds such as secondary metabolites [Hanson01].
Plants prefer the polyglutamylated forms of folates (compare folate polyglutamylation, glutamate removal from folates) since the turnover rate of those compounds is markedly increased [Cossins97] [Scott00] and meets the high demands for folates as observed in plants [Hanson02]. In addition the conjugated forms of folate facilitate the retention of the vitamin within the cell and its subcellular compartments [Appling91]. The plant enzymes involved in this pathway, although essentially catalyzing the same steps, have been found to differ in many regards from their bacterial counterparts [Cossins97] [Basset04a] [Basset04].
Folates are tripartite molecules and are made up of pterin, p-aminobenzoate (pPABA) and glutamate moieties. The one-carbon units are either attached to the N-5 of the pterin moietie, to the N-10 of the pPAPA moiety or are brigded in between those two (e.g. 5,10-methenyl or methylene-THF) [Basset05]. The different forms of folates are jointly connected and easily convertible into each other through a tight network of reactions (folate transformations I). Most of the enzymes have been identified in plants but some of them such as the formyltetrahydrofolate deformylase, presumably involved in the mutual conversion of tetrahydrofolate and its 10-formyl derivative remain to be demonstrated.
Among the many folates N5-formyl-tetrahydrofolate is the most enigmatic compound involved in the folate biosynthesis. N5-formyl-tetrahydrofolate is the only folate derivative that does not serve as a cofactor in the C1-metabolism, but it is the most frequent and stable form of folates found in plants [Stover93]. Moreover, N5-formyl-tetrahydrofolate is known to inhibit most of the folate dependent enzymes at physiological concentrations. The biological role of this compound is still poorly understood but it has been discussed as factor involved in the regulation of essential biosynthetic steps such as the formation of serine during photorespiration [Goyer05, Roje02].
The complete set of folate enzymes is only present in mitochondria. However, the recent discovery that folylpolyglutamate synthases are present in cytosol, mitochondria and plastids with each of them encoded by a different gene in Arabidopsis thaliana [Ravanel01] points to the fact that at least parts of the pathway can be carried out independently in those compartments. Interestingly, the enzyme hydrolyzing the polyglutamylated folates (γ-glutamyl hydrolase) has been found to be an extracellular enzyme in plants [Huangpu96]. Consequently, the transport and exact conversion of folates and their derivatives within the different cell compartments and their regulation pattern remains to be clarified before successfully attempting the endeavor to genetically engineer this pathway.
Variants: 4-aminobenzoate biosynthesis , folate polyglutamylation , folate transformations I , glutamate removal from folates , N10-formyl-tetrahydrofolate biosynthesis , superpathway of tetrahydrofolate biosynthesis , superpathway of tetrahydrofolate biosynthesis and salvage , tetrahydrofolate biosynthesis , tetrahydrofolate salvage from 5,10-methenyltetrahydrofolate
Unification Links: AraCyc:PWY-3841
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