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MetNet - plant pathway - folate transformations II
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Pathway details: folate transformations II

General info Interaction details Linked pathways Protein-protein interactions
  Pathway was created on Mon Jul 29, 2013.
 Contributed by aracyc:
General information: Tetrahydrofolate (vitamin B9) and its derivatives, commonly termed folates, are vital cofactors for enzymes mediating one-carbon-transfer reactions . Folates are involved in a wide range of key metabolic functions including the biosynthesis of methionine, purines, thymidylate and panthotenate. In plants folates are also involved in photorespiration, amino acid metabolism and chloroplastic protein biosynthesis . The fluxes through C1 pathways mediated by folates are especially high for methylated compounds such as the secondary metabolites lignin, alkaloids and betaines and for primary metabolites such as choline, pectine and chlorophyll . Although the biosynthetic steps in microbial folate biosynthesis essentially mirror the plant variant several differences are noteworthy. In contrast to the bacteria pathway () which predominantly takes place in the cytosol, the plant variant of tetrahydrofolate and formyl-tetrahydrofolate biosynthesis is split between three subcellular compartments . Several plant enzymes involved in the tetrahydrofolate biosynthesis differ from their microbial counterparts with regard to functionality, regulation and composition . Plants prefer the polyglutamylated forms of folates (compare folate polyglutamylation I, folate polyglutamylation II) since the turnover rate of those compounds is markedly increased |CITS: [Scott00]| and meets the high demands for folates as observed in plants . In addition the conjugated forms of folate facilitate the retention of the vitamin within the cell and its subcellular compartments . Special information: Folates are tripartite molecules and are made up of pterin, p-aminobenzoate (pPABA) and glutamate moieties. In plants the pterin moiety is formed from GTP in the cytosol, which couples to pPABA (synthesized in plastids) in mitochondria followed by subsequent glutamylation and reduction steps which may take place in cytosol, mitochondria and plastids . 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) |CITS: [Basset05]|. The different forms of folates are jointly connected and easily convertible into each other through a tight network of reactions (folate transformations). Among the many folates 5-formyl-tetrahydrofolate (5-CHO-THF) is the most enigmatic compound involved in the folate biosynthesis. 5-CHO-THF 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 . Moreover, 5-CHO-THF 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 . 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 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 (gamma-glutamyl hydrolase) has been found to be an extracellular enzyme in plants . 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.
  Parts of this pathway occur in:   cytosol     plastid     nucleus     mitochondrion   multiple locations  

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Enzymatic reaction
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metabolite [35]
protein complex [16]
RNA [43]
polypeptide [45]
gene [43]

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