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MetaCyc Pathway: L-ascorbate biosynthesis II (L-gulose pathway)
Inferred from experiment

Enzyme View:

Pathway diagram: L-ascorbate biosynthesis II (L-gulose pathway)

This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.

Synonyms: vitamin C biosynthesis, L-ascorbic acid biosynthesis II

Superclasses: BiosynthesisCofactors, Prosthetic Groups, Electron Carriers BiosynthesisVitamins BiosynthesisAscorbate Biosynthesis

Some taxa known to possess this pathway include : Arabidopsis thaliana col, Oryza sativa, Solanum tuberosum

Expected Taxonomic Range: Viridiplantae

Ascorbate (vitamin C) is an important antioxidant and an enzyme cofactor. Higher plants and higher animals (but not humans) can synthesize ascorbate. Plants provide the major dietary vitamin C source for humans. The plant ascorbate biosynthesis pathways have only been recently proposed. They differ from what was found in mammals.

About the different routes of ascorbate biosynthesis in plants:

The existence of alternative ascorbate biosynthesis routes in plants and the contribution of each route to ascorbate biosynthesis in vivo have been under debate. Wheeler et al originally proposed a so called linear L-galactose pathway (see L-ascorbate biosynthesis I (L-galactose pathway)) that requires the enzymes PMI (phosphomannose isomerase), PMM (phosphomannomutase) and VTC1 (GDP-D-mannose pyrophosphorylase) among the others [Wheeler98]. The failure to detect PMI activity in many plants in the past has prompted the search for alternative routes and the subsequent proposal of the L-gulose pathway (see L-ascorbate biosynthesis II (L-gulose pathway)) [Wolucka03]. However, the recent detection of PMI activity in Arabidopsis, the lower ascorbate contents observed in a PMI silenced line of tobacco, the higher ascorbate contents obtained in a PMI over-expressing line, and the lower ascorbate levels in the Arabidopsis VTC1 mutants all argue in favor of the linear L-galactose pathway (reviewed in [Linster08]).

About This Pathway

GDP-D-mannose 3",5"-epimerase converts GDP-D-mannose not only to GDP-L-galactose, an intermediate in the L-galactose pathway, but also to GDP-L-gulose. This finding prompted the proposal of the L-gulose pathway. Further more, feeding Arabidopsis cells with L-gulose or L-gulose-1,4-lactone increased ascorbate level. It again supports the existence of the L-gulose route [Wolucka03]. The L-galactose dehydrogenase purified from pea was shown active with L-gulose, although the enzyme's substrate specificity with L-gulose (Km= 3.7 mM) was very low comparing with its preferred substrate L-galactose (Km= 0.43 mM) [Gatzek02]. It remains to be determined whether it is has a biological role in the L-gulose pathway. L-gulose-1,4-lactone dehydrogenase activity was detected in potato tubers, in both the mitochondrial and cytosolic cell fractions [Wolucka03].

Variants: L-ascorbate biosynthesis I (L-galactose pathway), L-ascorbate biosynthesis III, L-ascorbate biosynthesis IV, L-ascorbate biosynthesis V, L-ascorbate biosynthesis VI (engineered pathway)

Created 03-Dec-2008 by Zhang P, TAIR


Gatzek02: Gatzek S, Wheeler GL, Smirnoff N (2002). "Antisense suppression of l-galactose dehydrogenase in Arabidopsis thaliana provides evidence for its role in ascorbate synthesis and reveals light modulated l-galactose synthesis." Plant J 30(5);541-53. PMID: 12047629

Linster08: Linster CL, Clarke SG (2008). "l-Ascorbate biosynthesis in higher plants: the role of VTC2." Trends Plant Sci 13(11);567-73. PMID: 18824398

Wheeler98: Wheeler GL, Jones MA, Smirnoff N (1998). "The biosynthetic pathway of vitamin C in higher plants." Nature 393(6683);365-9. PMID: 9620799

Wolucka03: Wolucka BA, Van Montagu M (2003). "GDP-mannose 3',5'-epimerase forms GDP-L-gulose, a putative intermediate for the de novo biosynthesis of vitamin C in plants." J Biol Chem 278(48);47483-90. PMID: 12954627

Other References Related to Enzymes, Genes, Subpathways, and Substrates of this Pathway

Ambler91: Ambler RP (1991). "Sequence variability in bacterial cytochromes c." Biochim Biophys Acta 1058(1);42-7. PMID: 1646017

Green05: Green MA, Fry SC (2005). "Vitamin C degradation in plant cells via enzymatic hydrolysis of 4-O-oxalyl-L-threonate." Nature 433(7021);83-7. PMID: 15608627

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

Major05: Major LL, Wolucka BA, Naismith JH (2005). "Structure and function of GDP-mannose-3',5'-epimerase: an enzyme which performs three chemical reactions at the same active site." J Am Chem Soc 127(51);18309-20. PMID: 16366586

Simpson00: Simpson GL, Ortwerth BJ (2000). "The non-oxidative degradation of ascorbic acid at physiological conditions." Biochim Biophys Acta 1501(1);12-24. PMID: 10727845

Watanabe06: Watanabe K, Suzuki K, Kitamura S (2006). "Characterization of a GDP-d-mannose 3'',5''-epimerase from rice." Phytochemistry 67(4);338-46. PMID: 16413588

Wolucka01: Wolucka BA, Persiau G, Van Doorsselaere J, Davey MW, Demol H, Vandekerckhove J, Van Montagu M, Zabeau M, Boerjan W (2001). "Partial purification and identification of GDP-mannose 3",5"-epimerase of Arabidopsis thaliana, a key enzyme of the plant vitamin C pathway." Proc Natl Acad Sci U S A 98(26);14843-8. PMID: 11752432

Wolucka06: Wolucka BA, Communi D (2006). "Mycobacterium tuberculosis possesses a functional enzyme for the synthesis of vitamin C, L-gulono-1,4-lactone dehydrogenase." FEBS J 273(19);4435-45. PMID: 16956367

Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by SRI International Pathway Tools version 19.5 on Sat Apr 30, 2016, BIOCYC11A.