title: Evidence for folate-salvage reactions in plants.
abstract: Folates in vivo undergo oxidative cleavage, giving pterin and p-aminobenzoylglutamate (pABAGlu) moieties. These breakdown products are excreted in animals, but their fate is unclear in microorganisms and unknown in plants. As indirect evidence from this and previous studies strongly suggests that plants can have high folate-breakdown rates (approximately 10% per day), salvage of the cleavage products seems likely. Four sets of observations support this possibility. First, cleavage products do not normally accumulate: pools of pABAGlu (including its polyglutamyl forms) are equivalent to, at most, 4-14% of typical total folate pools in Arabidopsis thaliana, Lycopersicon esculentum and Pisum sativum tissues. Pools of the pterin oxidation end-product pterin-6-carboxylate are, likewise, fairly small (3-37%) relative to total folate pools. Second, little pABAGlu built up in A. thaliana plantlets when net folate breakdown was induced by blocking folate synthesis with sulfanilamide. Third, A. thaliana and L. esculentum tissues readily converted supplied breakdown products to folate synthesis precursors: pABAGlu was hydrolysed to p-aminobenzoate and glutamate, and dihydropterin-6-aldehyde was reduced to 6-hydroxymethyldihydropterin. Fourth, both these reactions were detected in vitro; the reduction used NADPH as cofactor. An alternative salvage route for pABAGlu, direct reincorporation into dihydrofolate via the action of dihydropteroate synthase, appears implausible from the properties of this enzyme. We conclude that plants are excellent organisms in which to explore the biochemistry of folate salvage.
authors.affiliation: Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Orsomando
authors.forename: Gale G
authors.initials: GG
authors.lastname: Bozzo
authors.forename: Rocío Díaz
authors.initials: RD
authors.lastname: de la Garza
authors.forename: Gilles J
authors.initials: GJ
authors.lastname: Basset
authors.forename: Eoin P
authors.initials: EP
authors.lastname: Quinlivan
authors.forename: Valeria
authors.initials: V
authors.lastname: Naponelli
authors.forename: Fabrice
authors.initials: F
authors.lastname: Rébeillé
authors.forename: Stéphane
authors.initials: S
authors.lastname: Ravanel
authors.forename: Jesse F
authors.initials: JF
authors.lastname: Gregory
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Hanson
mesh_terms: D017360:Arabidopsis / Q000378:metabolism; D004094:Dihydropteroate Synthase / Q000378:metabolism; D005492:Folic Acid / Q000737:chemistry / Q000378:metabolism*; D005971:Glutamates / Q000737:chemistry / Q000378:metabolism; D006868:Hydrolysis; D018551:Solanum lycopersicum / Q000378:metabolism; D018532:Pisum sativum / Q000378:metabolism; D010944:Plants / Q000378:metabolism*; D011622:Pterins / Q000737:chemistry / Q000378:metabolism
chemical_list: D005971:Glutamates; D011622:Pterins; D005492:Folic Acid; C011398:4-aminobenzoylglutamic acid; D004094:Dihydropteroate Synthase