Arabinogalactan
Main page |
| Other names/abbreviations: | Larch Gum Stractan |
| Material type: | Polymer | |
| Material group: | Hetero polysaccharide, branched (Branch-on-branch) | |
| Monomer(s): | L-arabinofuranose L-arabinopyranose D-galactopyranose galactopyranosyl |
D-glucopyranosyl uronic acid D-glucose L-rhamnose D-xylose |
| Links: | alpha-(1-5) beta-(1-3) beta-(1-4) beta-(1-6) | |
| Origin of the polymer: | Natural | |
| CAS-Number: | 9036-66-2 | |
Structure
Two types of arabinogalactan:Type I: (→1)-β-D-galactose(4→) (main chain), (→1)-α-L-arabinose(5→) (side chain) linked at main chain C(3) [3].
Type II: (→1)-β-D-galactopyranose(3→) (main chain) and (→1)-β-D-galactopyranose-(6→) (side chain on virtually all units in the main chain) or (→1)-α-L-arabinofuranose(3→) (less frequent) or (→1)-D-glucopyranosyl uronic acid(6→) (least frequent). The β-D-galactopyranose and α-L-arabinofuranose substituents are in turn substituted by (→1)-β-D-glucopyranose-(6→) and (→1)-β-L-arabinopyranose-(3→) respectively, to give two-unit side-chain on almost every main chain residue [3]. Arabinogalactan is devoid of repeating units, but contains motifs, linkage and composition is highly dependent on the source [4]. The arabinogalactan from Mycobacterium tuberculosis contains five domains [6].
Larch arabinogalactan contains a polymer of (1→3)-β-linked D-galactopyranosyl as the main chain. Some of the units are replaced by (1→6)-linked L-arabinopyranose residues or by (1→6)-linked D-galactopyranose residues. Some of the D-galactosyl side chains, in turn, are substituted with a (1→3)-linked L-arabinofuracyl unit [11]. The L-arabinose to D-galactose ratio is 1:6 [11].
In soybean, the arabinogalactan consists of a (1→4)-β-linked D-galactopyranose backbone with substitution, every fourth or fifth residue, by (1→5)-α-linked D-arabinofuranose.
Urkonan A, B and C are composed of L-arabinose, D-xylose, D-galactose, D-glucose, L-rhamnose and D-galacturonic acid in the ratios A - 12:4:12:1:10. B - 12:4:12:1:2:4. C - 8:3:6:14:2:3 [2].
Most arabinogalactan samples are diversible into two fractions: A with M~100,000 and B with M~16,000. The 100,000-weight fraction is 67-90% [1]. True arabinogalactans have considerably higher molecular weights: 180.000-900.000 [5].
Chemical properties
Behavior in solutionArabinogalactan is highly soluble, and contrary to ordinary hydrocolloids gives low viscousity at low concentrations. pH in solution is 4.0-4.5. Solutions of arabinogalactan can be as high as 60% and can withstand the addition of up to 70% alcohol without precipitation. The viscousity of arabinogalactan is not affected very much by pH and electrolytes. Arabinogalactan substantially reduces the surface tension of water solution as well as the interfacial tension between water and oil mixtures. This makes arabinogalactan a very effective emulsifying agent [1].
Arabinogalactans can contain covalently linked proteins [5,9].
Behavior with other polymers
No specific adhesion to cellulose has been observed [12].
Arabinogalactan does not adhere signicantly (<5%) to curdlan [13].
Biological properties
Ukonan C is phagocytosis-activating, anti-complementary and alkaline phosphatase-inducing [2].Attached to a peptidoglycan thru a phosphodiester link in mycobacteria, involving the special linker (→4)-Rhap-(1→3)-GlcNAc-(1→P→6)-MurUA-(6→) [4]. The arabinogalactan from Mycobacterium tuberculosis show antigenic activity. This is from the arabinysyl residues, largely from fractions containing 2-linked arabinosylresidues [6].
Arabinogalactan II is found joined to hydroxyproline rich proteins, indicating, that it can form a point of union between polysaccharides of the cell and proteins [8].
Intravenous arabinogalactan from Larix occidentalis ends in the liver. It has therefore been tested as a hepatic drug delivery agent [9].
Molecular biology
10-35% inhibition on the restriction enzyme HindIII at 100 μg polysaccharide / μg λ DNA, and 75-95% inhibition at 500 μg polysaccharide / μg λ DNA [10].
Physical properties
Appearance | ||
| Physical state @ 20°C: | Solid | |
Bulk properties | ||
| Molecular weight (g/mol): | 180.000-900.000 [5] | |
Occurence, isolation & synthesis
OccurenceLarchwood, Larix occidentalis [11], Actinomycetes [4].
References
1: Glicksman,M. Gum Technology in the Food Industry(1969) Academic Press
2: Gonda,R., Tomoda,M., Ohara,N., Takada,K. Arabinogalactan Core Structure and Immunological Activities of Ukonan C, an Acidic Polysaccharide from the Rhizome of Curcuma longa
Biol. Pharm. Bull. (1993) 16 235-238
3: Mark,H.F., Bikales,N.M., Overberger,C.G., Menges,G., Kroschwitz,J.I. Encyclopedia of Polymer Science and Engineering 2.ed.
(1988) John Wiley & Sons
4: Daffe,M., McNeil,M., Brennan,P.J. Major Structural Features of the Cell Wall Arabinogalactans of Mycobacterium, Rhodococcus, and Nocardia spp.
Carbohydr. Res. (1993) 246 383-398
5: E.Jordan, H.Wagner. Structure and Properties of Polysaccharides from Viscum album (L.)
Oncology (1986) 43 Suppl 1 8-15
6: Daffe,M., Brennan,P.J., McNeil,M. Predominant Structural Features of the Cell Wall Arabinogalactan of Mycobacterium tuberculosis as Revealed Through Characterization of Oligoglycosyl Alditol Fragments by Gas Chromatography/Mass Spectrometry and by 1H and 13C NMR Analyses
J. Biol. Chem. (1990) 265 6734-6743
8: Heredia,A., Jiménez,A., Guillén,R. Composition of Plant Cell Walls
Z. Lebensm. Unters. Forsch. (1995) 200 24-31
9: Groman,E.V., Enriquez,P.M., Jung,C., Josephson,L. Arabinogalactan for Hepatic Drug Delivery
Bioconjug. Chem. (1994) 5 547-556
10: Do,N., Adams,R.P. A simple technique for removing plant polysaccharide contaminants from DNA
Biotechniques (1991) 10 162-166
11: White,E.V. The constitution of arabo-galactan. II. The isolation of heptamethyl- and octamethyl-6-galactosidegalactose through partial hydrolysis of methylated arabogalactan
J. Am. Chem. Soc. (1942) 64 302-306
12: Mishima,T., Hisamatsu,M., York,W.S., Teranishi,K., Yamada,T. Adhesion of ß-D-glucans to cellulose
Carbohydr. Res. (1998) 308 (3-4) 389-396
13: Hisamatsu,M., Mishima,T., Teranishi,K., Yamada,T. The correlation between adhesion of schizophyllan to yeast glucan and its effect on regeneration of yeast protoplast
Carbohydr. Res. (1997) 298 (1-2) 117-121
© Michael Pilgaard
Created: March 4, 2008