CONSTITUTION AND ARCHITECTURE IN THE CELL WALL 19 



Table 4. Hemicellulosic Aldobiuronic Acids 



Uronic Acid 



Aldose 



Linkage 



Source 



a-Glucuronic 

 a-Glucuronic 



4-O-Methyl-a-glucuronic 



4-O-Methyl-a-glucuronic 



4-O-Methyl-a-glucuronic 



3-O-Methyl-a-glucuronic 



^-Glucuronic 



[3-Glucuronic 



Galacturonic 



4-O-Methylglucuronic 



Maize (cob) 

 Wheat (straw), pear 



(fruit), sunflower (head) 

 Beech, birch, elm, pine, 



cedar, hemlock, maize, 



wheat 



Pine, wheat, (straw) 

 Cottonwood 

 Jute 



Gums (cherry, damson) 

 Gums (acacia, almond) 

 Mucilage (elm, flax, 



plantain) 

 Gum (lemon) 



L-arabinose 



D-xylose 



D-galactose 



L-galactose 



(3-D-galactopy ranosyl- 1 ,4-D-xylose 



D-a-xylopyranosyl-l,4-D-a-glu- 



copyran-osyluronic acid 

 D-xylopyranosyl- 1 ,3-L-arabinose 

 L-galactopyranosyl- 1 ,4-D-xylo- 

 pyranosyl- 1 ,2-L-arabinose 



The molecule containing these units has a xylan nucleus with 

 branch elements consisting of xylo-arabinose, galacto-xylo-arabinose, 

 glucuronic acid, and D-galactose. Both d- and L-galactose also 

 occur as end groups. 



One of the several maize cob hemicelluloses consists of highly 

 branched molecules, degree of polymerization (DP) 150, contain- 

 ing about 59 per cent D-xylose, 1 22 per cent L-arbinose, 11 per cent 

 methylglucuronic acid, and 8 per cent D-galactose. Glucuronic 

 acid and galactose occur only as non-reducing end units. 

 There are ten branch chains for every forty-four-unit linear chain, 

 and one glucuronic acid end group for each nine to eleven sugar 

 residues. 



