Arabinogalactans rhamnose

Fig. 2 Average structure of the hairy or ramified region of an apectic substance, with a rhamnogalacturonan I backbone substituted at position 4 of the rhamnose units with arabinan and arabinogalactan type II side chains...

Black pepper contains several polysaccharides of which one shows a strong effect as an immune enhancer based on the fact that the polymer is an anti-complementary polysaccharide. The polysaccharide has an Mw of approx. 40 kD. It is composed basically of rhamnose, arabinose, galactose and galac-turonic acid, and shows a high binding capacity for the Yariv reagent. This indicates that the side chain of the polymer is of the arabinogalactan type II, which is a common structure for several polysaccharides with an effect on the complement system [70]. 

Figure 1. Schematic representation of pectin structure indicating stabilization of catenated polygalacturonic acid chains through Ca + (O) cross-bridging. Non-bridging sequences of a(l-4) linked /S-galacturonic acid methylester extend from L-rhamnose via (1-4) linkage to another rhamnose via a(l-2) linkages. Arabinogalactan side chains are linked to rhamnose residues and couple the RG structure to hemicellulose.

The rhamnogalacturonan zones of acid pectic substances generally have lateral chains of neutral OSes, connected to carbon 4 of the rhamnose. For this reason, they are known as bristled zones , as opposed to the smooth zones of homogalactur-onan that do not branch off (Figure 3.18). There are two types of lateral chains in the bristled zones arabinogalactans in the majority (AG-II) and arabinans (A). 

Barrett and Northcote (1965) extracted apple fruit pectin under mild conditions and separated the neutral arabinogalactan fraction from the pectinic acid by differential precipitation. The purity of the fractions was monitored by zone electrophoresis. It was found that the purified pectinic acid contained galactose, arabinose, rhamnose, xylose, fucose, 2- C methyl xylose... 

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