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.
|Superclasses:||Biosynthesis → Carbohydrates Biosynthesis → Sugars Biosynthesis → Sugar Nucleotides Biosynthesis → GDP-sugar Biosynthesis|
Expected Taxonomic Range: Embryophyta
GDP-L-galactose is a nucleotide-sugar that is used as biosynthetic precursor of L-galactosyl residues in polysaccharides and oligosaccharides in plants [Seifert04, Reuhs04]. The L-galactosyl residues of cell wall polysaccharides, as well as those of glycoproteins only represent relatively minor components of those compounds, which helps explain the relative scarcity of information available concerning their biosynthesis. Importantly, GDP-L-galactose is also used in L-ascorbate biosynthesis I (L-galactose pathway) in plants.
Enzymatic steps: The key enzyme for the conversion of GDP-D-mannose to GDP-L-galactose is the bifunctional GDP-D-mannose 3",5"-epimerase (GME) which catalyzes the reversible, dual epimerization of GDP-D-mannose into both GDP-L-galactose and GDP-L-gulose [Wolucka03, Watanabe06].
Unification Links: AraCyc:PWY-5115
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
Reuhs04: Reuhs BL, Glenn J, Stephens SB, Kim JS, Christie DB, Glushka JG, Zablackis E, Albersheim P, Darvill AG, O'Neill MA (2004). "l-Galactose replaces l-fucose in the pectic polysaccharide rhamnogalacturonan II synthesized by the l-fucose-deficient mur1 Arabidopsis mutant." Planta 219(1);147-57. PMID: 14991405
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
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
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