A-D-galacturonic acid

Pectin belongs to a family of plant polysaccharides in which the polymer backbone consists of (1— 4)-linked a-D-galacturonic acid repeating-units. Often, (1— 2)-linked a-L-rhamnose residues interrupt the regular polygalacturonate sequence. The high viscosity and gelling properties of pectins are exploited by the food and pharmaceutical industries. X-Ray studies on sodium pectate, calcium pectate, pectic acid, and pectinic acid (methyl ester of pectic acid) have disclosed their structural details. 

The LPS from Proteus species contain amino acids linked as amides to acidic sugars. Thus, L-lysine is linked by way of N-6 to a D-galacturonic acid residue (52) in the LPS from P. hauseri, but by way of N-2 to a D-glucu-ronic acid residue in the LPS from P. mirabilis 027. The latter LPS also contains L-alanine, linked to the carboxyl group of a D-galacturonic acid residue. 

In the course of studies on the physicochemical properties of natural polymers in aqueous solution, attention has been drawn to pectic acid, i.e. poly (a-D)galacturonic acid as a potential model of a rigid polysaccharide. 

Extensive data are given in the Uterature for the potentiometric titration of polymer acids which may be used to study the behaviour of polyelectrolyte systems under different conditions. For poly(a-D) galacturonic acid there are few data of this kind, especially in connection with the occurrence of a conformational transition induced by pH variations, or with the effect brought about by the addition or the exchange of counterions. Since for a polyacid not exhibiting a conformational transition in the course of titration, pK K denoting the apparent dissociation constant) increases monotonously with degree... 

The purpose of this study is to consider in more detail the influence of the size and nature of the counterion on the degree and extent of dissociation of poly(a-D)galacturonic acid already discussed in a previous paper [2], particularly to check the effect of screening the charges on the polyacid in the presence of different counterions. 

Commercially available poly(a-D)galacturonic acid PGA) was purchased from Fluka Chemie. To obtain an aqueous solution of the polyacid, insoluble PGA was converted to its soluble sodium salt and then percolated through a cation-exchange resin in the H-form [3]. 

It is now clear that the basic skeletons of all pectic substances consist essentially of poly-a-D-galacturonic acids the constituent units of which contain the pyranose ring and are linked glycosidically in a configuration through positions 1 and 4.s 6... 

In potato pectic polysaccharides, the RG-I domain accounts for 75% of the total, a much higher proportion than in pectic polysaccharides of other species ( 20-35%) (Oomen et al., 2003 Mohnen et al., 2008). RG-1 consists of a backbone of alternating a-D-galacturonic acid and a-L-rhamnosyl residues, linked as indicated in Figure 3.3, which in potato accounts for 14% of the total RG-1 (Oomen et al., 2003). Although the galacturonic acid residues are probably not methyl-esterified, they may be acetylated. This is so in potato, where a preparation... 

Prepare a D-galacturonic acid standard curve with each batch of samples. 

L-fhreo-Pentos-2-ulose (9) was prepared by several procedures (see Scheme 3). In procedure A, D-galacturonic acid (14) was reduced with sodium amalgam to L-galactonic acid (15), which lactonized to L-ga-lactono-1,4-lactone (16) by removal of water. Treatment of 16 with ammonia in methanol afforded L-galactonamide (17) which, on oxidation with sodium hypochlorite, gave L-lyxose (18). Reaction of 18 with phenylhydrazine yielded the corresponding osazone (19) which, on hydrolysis, afforded 9. 

Lamberth and co-workers [23] synthesized several chiral mandelamides in a Passerini reaction of 1,2,3,4-tetra-O-acetyl-a-D-galacturonic acid with achiral benzal-dehydes and isocyanides (Scheme 9.15). 

Agius, F., Gonzales-Lamonthe, R., Caballero, J.L., Munoz-Bianco, J., Botella, M.A., and Valpuesta, V, 2003, Engineering increased vitamin C levels in plants by overexpression of a D-galacturonic acid reductase. Nat. Biotechnol. 21 177-181. 

Crystalline a-D-galacturonic acid monohydrate has been studied by C CPMAS NMR and X-ray crystallography. The molecular dynamics have been investigated by evaluating C spin-lattice relaxation in the rotating frame (Tip) and CSA properties of each carbon. It has been found that only limited molecular motions can be detected in the low frequency (<10 Hz) range by Tip( C) measurements and changes of CSA properties as a function of temperature. 

Pectins from plant cell walls contain partially methyl esterified a-D-galacturonic acid (Doesburg, 1966), and several methods are available for the determination of their methyl ester content (Doesburg, 1966). 

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