Polygalacturonate

Pectin. Pectin [9000-69-5] is a generic term for a group of polysaccharides, mainly partially methoxylated polygalacturonic acids, which are located in the cell walls of all plant tissues. The main commercial sources of pectin are citms peel and apple pomace, where it represents 20—40% and 10—20% of the dry weight respectively. The pectin is extracted, the extract purified, and the pectin precipitated (50) increased extraction times lead to the production of low methoxyl pectins. 

QuinidJne. Quinidine, an alkaloid obtained from cinchona bark (Sinchona sp.), is the dextrorotatory stereoisomer of quinine [130-95-0] (see Alkaloids). The first use of quinidine for the treatment of atrial fibrillation was reported in 1918 (12). The sulfate, gluconate, and polygalacturonate salts are used in clinical practice. The dmg is given mainly by the oral (po) route, rarely by the intravenous (iv) route of adniinistration. It is the most frequentiy prescribed po antiarrhythmic agent in the United States. The clinical uses of quinidine include suppression of atrial and ventricular extrasystoles and serious ventricular arrhythmias (1 3). 

The pH of the reaction mixture is taken both before and after the addition of the last portion of the quinidine-methanol solution. The mixture is gently warmed (30° to 50°C), and the pH determined at 20 minute intervals. At the end of 4 hours, or when the reaction has gone to completion as evidenced by the pH of the mixture (between pH 6.5 and 7.5), the stirring is then stopped and the mixture cooled to 0°C and filtered. The solvent is evaporated to dryness under reduced pressure, utilizing as little heat as is feasible. The dried residue Is powdered and suspended in 10 volumes of methanol and filtered. The insoluble powder is dried, and is quinidine polygalacturonate, melting at 180°C with decomposition. 

Pectin is a collective name for heteropolysaccharides, which consist essentially of polygalacturon acid. Pectin is soluble in water only after a partial neutralization with alkali or ammonium hydroxide [18]. 

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 possible involvement of polygalacturonic acid-containing molecules in the defence reactions of tomato root cells against Fusarium oxysporum was suggested about 20 years ago by their accumulation at penetration sites. Since papillae are held to serve as a resistance mechanism to fungal penetration, it was assumed that the interrelation between pectin and other polymers - such as lignin - may contribute to enhancing the hardness of these newly formed structures (Benhamou et al., 1990). 

The source materials were commercial pectins apple A30 and citrus pectin C73 kindly supplied by Unipectine (France) and Copenhagen Pectin Factory (Denmark) respectively. Polygalacturonic acid samples (named SR) were obtained by acid hydrolysis of a fully de-esterified citrus pectin as previously described [24]. Citrus pectins with different degree of esterification (DE) were obtained by controlled acid de-esterification [8]. 

Fig 4 FTIR spectra of walls of DCB-adapted and non-adapted tomato suspension cells, onion parenchyma cell walls, and polygalacturonic acid (Sigma), a = ester peak, b = free acid stretches from pectins, y axis is absorbance, X axis is wavenumber (frequency inverse). 

The Fourier Trairsform Infrared (FTIR) spectrum obtained from non-adapted tomato cell walls is very similar to that from the onion parenchyma cell wall (both contain cellulose, xyloglucan and pectin) although there is more protein in the tomato walls (amide stretches at 1550 and 1650 cm-i) (Fig 4). In DCB-adapted tomato cell walls, the spectrum more closely resembles that of either purified pectins or of a commercial polygalacturonic acid sample from Sigma with peaks in common at 1140, 1095, 1070, 1015 and 950 cm-t in the carbohydrate region of the spectrum as well as the free acid stretches at 1600 and 1414 cm-i and an ester peak at 1725 cm-k An ester band at 1740 cm-i is evident in both onion parenchyma and non-adapted tomato cell wall samples. It is possible that this shift in the ester peak simply reflects the different local molecular environment of this bond, but it is also possible that a different ester is made in the DCB-adapted cell walls, as phenolic esters absorb around 1720 cm-i whilst carboxylic esters absorb at 1740 cm-k The... 

BolweU, G.P., Dalessandro, G., and Northcote, D.H. (1985) Decrease of polygalacturonic acid synthase during xylem differentiation in sycamore. Phytochemistry, 24 699-702. 

Doong, R.L., liljebjelke, K., FraUsh, G., Kumar, A., and Mohnen, D. (1995) CeU-free synthesis of pectin Identification and partial characterization of polygalacturonate 4-a-galacturonosyltransferase and its products fix)m membrane preparations of tobacco ceU-suspension cultures. Plant Physiol. 109 141-152. 

ViUemez, C.L., Lin, T.-Y., and Hassid, W.Z. (1965) Biosynthesis of the polygalacturonic acid chain of pectin by a particulate enzyme preparation from phaseolus aureus seedlings. Proc.Natl.Acad.Sci.USA, 54 1626-1632. 

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