The Uronic Acids

The L-arabino-(4-0-methyl-D-glucurono)xylans are found in softwoods and annual plants. The L-arabinose is present primarily as a-L-arabinofuranosyl units, although P-L-arabinopyranosyl units may also be present. In either case, the arabinosyl units are often, but not always, present as single-unit side chains, as are the uronic acid units. 

The first paper on the bioactive polysaccharides from Glycyrrhiza uralensis roots was published in 1996 by Kiyohara et al. [57]. They isolated a pectic type polymer with anti-complementary and mitogenic activity that was an acidic pectin, possibly containing rhamnogalacturonan type I as part of the total structure. Degradation of the uronic acid part of the molecule decreased both types of bio activities. The neutral oligosaccharide chains were shown to retain some of the activities of the native polymer, but it was suggested that they should be attached to the acidic core to retain maximum activity. 

GLUCURONATE, A PRECURSOR OF PROTEOGLYCANS CONJUGATED GLUCURONIDES, IS A PRODUCT OF THE URONIC ACID PATHWAY... 

Disruption of the Uronic Acid Pathway Is Caused by Enzyme Defects Some Drugs... 

The uronic acid pathway is the source of glucuronic acid for conjugation of many endogenous and exogenous substances before excretion as glucuronides in urine and bile. 

Vitamin C (Figure 45-19) is a vitamin for human beings and other primates, the guinea pig, bats, passerine birds, and most fishes and invertebrates other animals synthesize it as an intermediate in the uronic acid pathway of glucose metabohsm (Chapter 20). In those species for which it is a vitamin, there is a block in that pathway due to absence of gulonolactone oxidase. Both ascorbic acid and dehydroascorbic acid have vitamin activity. 

As the copper content of cell walls increases, the Cu " ions distribute between the two types of uronates most of them on high affinity sites first, at low copper contents more on low affinity sites afterwards. The percentage of the uronic acids that bind Cu with a high affinity is plotted on Fig. 5 as a function of the relative amount of copper in the walls. We can see that about 30% of the uronic acids consist of high affinity sites. 

Reduction of uronic acids Uronic acids (UA) were converted to the corresponding neutral sugars (NS) by carbodiimide activation of the carboxyl groups followed by a reduction with NaBD4 according to the method of Kim and Carpita [5]. In order to achieve a complete reduction of the uronic acids the procedure was repeated once. 

Glycosidic linkage composition of the uronic acid residues in fraction N1... 

Kim, J-B., Caipita, N.C. (1992), Changes in esterification of the uronic acid groups of cell wall polysaccharides during elongation of maize coleoptiles. Plant Physiol. 98, 646-653. 

The uronic acids in polysaccharide fraction I (Table 2) were determined colorimetrically with m-hydroxybiphenyl (15). 

Although the glycosidic bonds of uronic acid residues are usually more resistant to acid hydrolysis than those of neutral polysaccharides,218 these linkages in heparin are more readily cleavable then those between the hexosamine and the uronic acid residues. Disaccharides obtained by exhaustive hydrolysis of heparin with 0.5 MHC1 at 80° contained hexu-... 

Influence of Metal Ions on Oxygen Chemisorption and Ignition of Chars. We have carried out extensive studies of the influence of metal ions in wood on pyrolysis mechanisms (5.6) and this approach has now been extended to oxygen chemisorption of the chars. The metal ions occur in wood predominantly as the counterions of the uronic acid components of the hemicelluloses (12). We have shown that they can be almost completely removed by very mild acid treatment without any other major change in the chemistry of the wood. Table II shows that the major metal ions in cottonwood are Ca, K and Mg. The acid-washing process removed 98X of the metal ions in... 

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