Note: a dashed line (without arrowheads) between two compound names is meant to imply that the two names are just different instantiations of the same compound -- i.e. one may be a specific name and the other a general name, or they may both represent the same compound in different stages of a polymerization-type 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: pectin biosynthesis
|Superclasses:||Biosynthesis → Carbohydrates Biosynthesis → Polysaccharides Biosynthesis|
|Biosynthesis → Cell Structures Biosynthesis → Plant Cell Structures → Primary Cell Wall|
Expected Taxonomic Range: Embryophyta
Homogalacturonan (HGA) is a linear chain of 1,4-linked a-D-galacturonic acid residues in which some of the carboxyl groups are methyl esterified. HGA accounts for up to 60% of the pectin found in primary cell walls of all plants.
To synthesize HGA, UDP-galacturonate is formed from UDP-glucuronate in the cytosol. UDP- galacturonate is then transported into the Golgi by a proposed UDP- galacturonate:UMP antiporter. The galacturonate residue is transferred onto a growing HGA chain. Some of the newly added galacturonate residues are methyl esterifed at the C-6 carboxyl group. Vesicles containing the newly synthesized HGA are targeted to and fuse with the plasmamembrane thereby releasing the HGA into the exocellular space for subsequent incorporation into the wall.
Unification Links: AraCyc:PWY-1061
Goubet99: Goubet F, Mohnen D (1999). "Solubilization and partial characterization of homogalacturonan-methyltransferase from microsomal membranes of suspension-cultured tobacco cells." Plant Physiol 121(1);281-90. PMID: 10482684
Henrik99: Henrik Vibe Scheller, Ron Lou Doong, Brent Lee Ridley, Debra Mohnen "Pectin biosynthesis: a solubilized alpha 1,4-galacturonosyltransferase from tobacco catalyzes the transfer of galacturonic acid from UDP-galacturonic acid onto the non-reducing end of homogalacturonan." Planta. 1999. 207:512-517.
Ron98: Ron Lou Doong, Debra Mohnen "Solubilization and characterization of a galacturonosyltransferase that synthesizes the pectin polysaccharide homogalacturonan." The Plant Journal. 1998. 13(3):363-374.
Sterling01: Sterling JD, Quigley HF, Orellana A, Mohnen D (2001). "The catalytic site of the pectin biosynthetic enzyme alpha-1,4-galacturonosyltransferase is located in the lumen of the Golgi." Plant Physiol 127(1);360-71. PMID: 11553763
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