MetaCyc Enzyme: UDP-D-glucuronic acid 4-epimerase

Gene: GAE4 Accession Number: AT2G45310 (MetaCyc)

Synonyms: UGlcAE1, UDP-D-GlcA 4-epimerase, UDP-D-glucuronate 4-epimerase, UDP-D-galacturonic acid 4-epimerase, UDP-D-galacturonate 4-epimerase, UDP-D-GalA 4-epimerase

Species: Arabidopsis thaliana col

Subunit composition of UDP-D-glucuronic acid 4-epimerase = [GAE4]2
         subunit of UDP-GlcA 4-epimerase = GAE4

This Arabidopsis thaliana enzyme (UGlcAE1) catalyzes the epimerization of UDP-α-D-glucuronate (UDP-GlcA) to UDP-α-D-galacturonate (UDP-GalA). The dimeric protein is encoded by the UGlcAE1 gene. Expression of the full-length gene in E.colifails to produce an active enzyme. It was postulated that the hydrophobic putative N-terminal transmembrane domain results in un- or misfolding of the protein in inclusion bodies [Gu04]. A partially purified recombinant UGlcAE1Δ1-64, lacking the transmembrane domain, however, could be expressed in E.coli and was shown to have a UDP-GlcA 4-epimerase catalytic activity [Gu04]. The reaction is reversible, but favours the formation of UDP-GalA over UDP-GlcA with an equilibrium constant of approximately 1.9. The enzyme does not require NAD+ or metal ions for activity, and maintains maximum activity in the presence of EDTA. The enzyme has a broad pH range (6.4 to 8.2) centered around 7.4-7.6. Activity is completely abolished at pH values lower than 4 and higher than 9.5 in phosphate buffer [Gu04]. The temperature range is also broad with enzyme activity between 25?C and 55?C with maximal activity between 30?C and 42?C. UDP-glucose and UDP-galactose had no inhibitory effect while UDP-xylose, UDP-arabinose and UDP were strong inhibitors.

Molecular Weight of Polypeptide: 43.5 kD (from nucleotide sequence)

Molecular Weight of Multimer: 88 kD (experimental) [Gu04]

Unification Links: Entrez:AAT06796 , ModBase:O22141 , PhylomeDB:O22141 , Pride:O22141 , Protein Model Portal:O22141 , SMR:O22141 , String:3702.AT2G45310.1-P , Swiss-Model:O22141 , TAIR:AT2G45310 , UniProt:O22141

Relationship Links: Entrez-Nucleotide:PART-OF:AY594693 , InterPro:IN-FAMILY:IPR001509 , InterPro:IN-FAMILY:IPR008089 , InterPro:IN-FAMILY:IPR016040 , Pfam:IN-FAMILY:PF01370 , Prints:IN-FAMILY:PR01713

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

Enzymatic reaction of: UDP-D-glucuronic acid 4-epimerase

EC Number:

UDP-α-D-glucuronate <=> UDP-α-D-galacturonate

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction of enzyme catalysis.

This reaction is reversible.

In Pathways: UDP-sugars interconversion , UDP-D-galacturonate biosynthesis I (from UDP-D-glucuronate)

Inhibitors (Unknown Mechanism): UDP-α-D-xylose [Gu04] , UDP [Gu04] , UDP-L-arabinose [Gu04] , potassium chloride [Gu04] , sodium chloride [Gu04]

Primary Physiological Regulators of Enzyme Activity: UDP-α-D-xylose , UDP , UDP-L-arabinose

Kinetic Parameters:

Km (μM)

T(opt): 36 °C [Gu04]

pH(opt): 7.5 [Gu04]


Gu04: Gu X, Bar-Peled M (2004). "The biosynthesis of UDP-galacturonic acid in plants. Functional cloning and characterization of Arabidopsis UDP-D-glucuronic acid 4-epimerase." Plant Physiol 136(4);4256-64. PMID: 15563616

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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 19.0 on Tue Oct 6, 2015, biocyc12.