Galacturonan region

From these results it was concluded that there is an intramolecular distribution in which the neutral sugar residues are concentrated in blocks of more highly substituted rhamno-galacturonan regions ("hairy"), separated by unsubstituted ("smooth") regions containing almost exclusively D-galactosyluronic residues (16)... 

Pectins are heteropolysaccharides with axial-axial a(1, 4)-D galactopyranosyluronic acid units condensed in the Ci conformation and interrupted by a-(1,2)-L rhamnopyranosyl residues. The structure is based on blocks of galacturonan partly esterified (the smooth zones) and blocks of highly ramified rhamnogalacturonan regions (hairy zones). The exact structure depends on the sources but also on the methods used to isolate the pectins [1,5]. Few data are given in Table 1. 

Figure 1. Schematic structure of apple pectin rhamno-galacturonan backbone with regions rich in neutral sugar side chains (hairy regions).

At present, a number of questions remain open. There is the specific question on the structure of the often branched side chains and the more general question on whether structural features are intra- or intermolecular phenomena. Do the molecules of a pectin preparation have smooth and hairy regions or is there a mixture of pure galac-turonan molecules and galacturonan molecules with many side chains How is the inter- and intramolecular distribution of methoxylated and free carboxyl groups ... 

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