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MetaCyc Compound Class: a glucuronoxylan

Synonyms: MGX, 4-O-methyl-D-glucurono-D-xylan

Superclasses: all carbohydrates a carbohydrate a glycan a polysaccharide hemicellulose xylan a (1->4)-beta-D-xylan

Summary:
Glucuronoxylans are a component of hemicellulose. They are linear polymers of β-D-xylopyranosyl units linked by (1→4) glycosidic bonds, with many of the xylose units substituted with 2,2 or 2,3-linked glucuronate residue, which are often methylated at position 4. Most of the glucuronoxylans have single 4-O-methyl-α-D-glucopyranosyl uronate residues (MeGlcA) attached at position 2. This structural type is usually named as 4-O-methyl-D-glucurono-D-xylan (MGX).

Angiosperm (hardwood) glucuronoxylans also have a high rate of substitution (70-80%) by acetyl groups, at position 2 and/or 3 of the β-D-xylopyranosyl, conferring on the xylan its partial solubility in water.

The ratio of xylosyl residues to D-glucuronate/4-O-methylglucuronate residues in glucuronoxylans varies greatly among species. An average ratio of 10:1 is accepted, although it can be as high as 2:1, for example, in quince (Cydonia oblonga) seeds [Vignon98].

Child Classes: a 2-O-α-D-galactopyranosyl-4-O-methyl-α-D-glucurono)-D-xylan (0) , a glucuronoxylan oligosaccharide (0)

SMILES: COC1(C(C(O)C(OC(C([O-])=O)1)OC4(C(OC2(COC(C(C2O)O)OC3(COC(C(C3O)O)O[R2])))OCC(C4O)OC5(C(C(C(CO5)OC6(C(C(C(CO6)OC7(C(C(C(CO7)O[R1])O)O))O)O))O)O)))O)

Reactions known to consume the compound:

xylan biosynthesis :
UDP-α-D-glucuronate + a (1→4)-β-D-xylana glucuronoxylan + UDP

Not in pathways:
a glucuronoxylan + H2O → 4-O-methyl-α-D-glucuronate + a (1→4)-β-D-xylan
a glucuronoxylan + n H2O → n a glucuronoxylan oligosaccharide

(1,4)-β-xylan degradation :
a (1→4)-β-D-xylan → a (1->4)-β-D-xylan oligosaccharide

cellulose and hemicellulose degradation (cellulolosome) :
a (1→4)-β-D-xylan + n H2O → n a (1->4)-β-D-xylan oligosaccharide

xylan biosynthesis :
UDP-β-L-arabinopyranose + a (1→4)-β-D-xylan → an arabinoxylan + UDP
UDP-α-D-xylose + [(1->4)-β-D-xylan](n) → UDP + [(1->4)-β-D-xylan](n+1)


xylan + n H2O → n α-D-xylopyranose


a polysaccharide + H2O → an oligosaccharide

Reactions known to produce the compound:

Not in pathways:
acetylxylan + n H2O → xylan + n acetate

cellulose and hemicellulose degradation (cellulolosome) :
a feruloyl-polysaccharide + H2O → ferulate + a polysaccharide + 2 H+


an N-acetyl-β-D-galactosalaminyl-[glycan] + H2O → a glycan + N-acetyl-β-D-galactosamine

Credits:
Created 06-Apr-2011 by Caspi R , SRI International


References

Vignon98: Vignon, M. R., Gey, C. (1998). "Isolation, 1H and 13C NMR studies of (4-O-methyl-D-glucurono)-D-xylans from luffa fruit fibres, jute bast fibres and mucilage of quince tree seeds." Carbohydrate Research 307(1-2):107-111.


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 18.5 on Thu Nov 27, 2014, biocyc11.