Pectic acids acetylated, preparation

A series of O-acetyl derivatives of pectic acid has been prepared to study the intramolecular binding of Ca + ions to pectic acids. The electrostatic free enthalpy of dissociation of these polyacids and the rate of exchange of the counter-ion from Ca + to K+ were determined by potentiometric titration measurements. The binding of Ca + ions was characterized by the production of single ion affinity coefficients determined in solutions of the calcium salts of 0-acetyl pectic acids and by the circular dichroism measurements of calcium and potassium salts of the pectate derivatives. The intramolecular binding of Ca + ions to isolated pectate macromolecules is purely of electrostatic character in contrast to the intermolecular chelate binding of Ca + ions which takes place when the pectate macromolecules aggregate. 

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... 

A large number (>50) of glycosyltransferases and other types of transferase are required to synthesize pectic polysaccharides [20]. The activities of several glycosyltransferases have been identified in cell-free membrane preparations from plants. However, only a few of these enzymes have been partially characterized and shown to be involved in pectin biosynthesis. These include D-galacturonosyl transferase, galactosyl transferase, arabinosyl transferase, and apiosyl transferase [20]. An enzyme that catalyzes the methylesterification of homogalacturonan (homogalatur-onan methyltransferase) has been partially characterized [20]. There are also reports that plants contain methyltransferases that catalyze the methylesterification of RG-I and RG-II [25]. No 0-acetyl transferase involved in pectin biosynthesis has been characterized nor have the enzymes that catalyze the addition of phenolic acids to pectins [20]. 

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