描述
Emulsifier, stabiliser
Approximately one of the three arabinosyl chains attached to the galactan chain contains succinyl groups. Although one succinyl group is most common, up to three succinyl groups per released arabinan fragment can be found on oligo-arabinans. However, arabinan fragments substituted with GalNH2 are not succinylated. Importantly, in the case of M. tuberculosis, and most likely in all slow growers, both positive charge (protonated GalNH2 as GalNH3+) and negative charge (succinyl) are present in the middle regions of the arabinan, specifically at O-2 of the inner 3,5-?-D-Araf units. The succinyl residues are on the non-mycolylated chain. Recently a complete primary model of arabinogalactan has been proposed.; Arabinogalactan is a biopolymer consisting of arabinose and galactose monosaccharides. Two classes of arabinogalctans are found in nature: plant arabinogalactan and microbial arabinogalactan. In plants, it is a major constituents of many gums, including gum arabic, gum gutti and so on. It occasionally attached to proteins and the resulted proteoglycan functions as signaling molecules betweens cells as well as glue to seal wounded part of plants.; The microbial arabinogalactan is a major structural component of the mycobacterial cell wall. Both the arabinose and galactose are solely in the furanose configuration. The galactan portion of the microbial arabinogalactan is linear, consisting of approximately 30 units with alternating ?-(1-5) and ?-(1-6) glycosidic linkages. The arabinan chain, which consist of about 30 residues, are attached at three branch points within the galactan chain (believed to be at residues 8, 10 and 12).The arabinan portion of the polymer is a complex branched structure, usually capped with mycolic acids. The arabinan glycosidic linkages are ?-(1-3), ?-(1-5), and ?-(1-2).; The non-reducing end of arabinogalactan is covalently attached to the mycolic acids of the outer membrane. The hydrophobicity of mycolic acids is a barrier to drug entry. Additionally, the mycolyl arabinogalactan peptidiglycan is responsible for aspects of disease pathogenesis and much of the antibody response in infections. The mycolyl substituents are selectively and equally distributed on the 5-hydroxyl functions of terminal- and the penultimate 2-linked Araf residues. The mycolyl residues are clustered in groups of four on the non reducing terminal pentaarabinosyl unit (?-Araf-(1?2)-?-Araf)2-3,5-?-Araf. Thus, the major part (66%) of the pentaarabinosyl units are substituted by mycolic acids, leaving the unsubstituted minor region (33%), that is available for interaction with the immune system.