Methyl esterified galacturonic acid

Pectins are important in cell wall assembly and detailed information of their structure will help to elucidate the relationship between the structures and physical properties. One possible approach is the chemical degradation of pectins. The specific degradation of the methyl esterified galacturonic acid residues of pectin to the corresponding... 

Needs, P. W., Rigby, N. M., Ring, S. G., MacDougall, A. J. Specific degradation of pectins via a carbodiimide-mediated Lessen rearrangement of methyl esterified galacturonic acid residues. Carbohydr. Res. 2001, 333,47-58. 

Scheme 4.32 Carbodiimide-mediated Lossen rearrangement of methyl-esterified galacturonic acid residues.

N. O. Maness, J. D. Ryan, and A. J. Mort, Determination of the degree of methyl esterification of pectins in small samples by selective reduction of esterified galacturonic acid to galactose, Anal. Biochem., 185 (1990) 346-352. 

Fig. 1. — Effect47 of Tomato Pectinesterase on the Activity of Pectate Lyase Acting on Highly Esterified Pectin. [Reaction mixtures contained 0.5% of D-galacturonan (broken line) or poly(D-galacturonic acid methyl ester) methyl glycoside (solid lines), 5 mM CaCl2, 33 mM phosphate buflFer (pH 7.0), and 0.25 unit of lyase in a final volume of 3.0 ml. In addition, the reaction mixture represented by the middle curve contained 0.031 unit of tomato pectinesterase in a final volume of 3.3 ml.] Reprinted, with permission, from M. Lee and J. D. Macmillan, Biochemistry, 9, 1930-1934 (1970). Copyright by the American Chemical Society.

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... 

Figure E3.4.1 Structure of galacturonic acid showing methyl esterified and acetylated forms.

D-Galacturonic acid residues, partially methyl esterified presence of 1,2-linked L-rhamnosyl residues... 

Pectin consists predominantly of sequences of galacturonic acid residues (which are quite similar to the G units in alginate), with occasional interruptions by rhamnose residues. At least some of the carboxyl groups are methyl esterified, the precise distribution depending upon the plant source and age, and an important aspect still not fully understood. Reasonably in view of their structural similarity, pectins of low degree of esterification behave like alginates, and gel with divalent ions. The more esterified materials gel under conditions of low pH and decreased water activity, Le. where intermolecular electrostatic repulsions are reduced in this case the junction zones are thermoreversible at, say, 40 C. 

Certain carboxylic acids, such as a-acylaminocarboxylic acids, or ketals of polyhydroxycarboxylic acids e.g. 1,2-3,4-diisopropylidene-D-galacturonic acid, can be esterified conveniently by simply heating their soln. in the respective alcohol under pressure at 180°, without use of a catalyst.—E A soln. of hippuric acid in methanol heated 10 hrs. at 180-185 under an initial pressure of 1000 lbs./sq.in./25° —y methyl hippurate. Y 82.5%. (F. e. s. H. Rinderknecht and C. Niemann, Am. Soc. 70, 2605 (1948) at atmospheric pressure s. W. J. Brehm and H. G. Lindwall, J. Org. Chem. 15, 685 (1950).)... 

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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