Chemical characterization of the immunomodulating polysaccharide of Aloe vera L.
The polysaccharide isolated by alcohol precipitation of Aloe vera mucilaginous gel was found to have a Man:Glc:Gal:GalA:Fuc:Ara:Xyl ratio of 120:9:6:3:2:2:1 with traces of Rha and GlcA. Linkage analysis of the endo-(1-->4)-beta-d-mannanase-treated sample yielded Manp-(1--> (approximately 26%), 4-Manp (approximately 53%), 2,4-Manp (approximately 3%), 3,4-Manp (approximately 1%), 4,6-Manp (approximately 1%), 4-Glcp (approximately 5%), 4-Xylp (approximately 1%), Xylp-(1--> (approximately 2%), Galp-(1--> (approximately 5%), and traces of 4,6-Galp and 3,6-Galp. Hydrolysis with strong acids produced a mixture of short oligosaccharides and an acid-resistant fraction containing greater relative fractions of Manp-(1-->, Araf-(1-->, Xylp-(1-->, and 4-Xylp than the bulk polysaccharide. NMR analysis of oligosaccharides generated by endo-(1-->4)-beta-D-mannanase and acid hydrolysis showed the presence of di-, tri-, and tetrasaccharides of 4-beta-Manp, beta-Glcp-(1-->4)-Man, beta-Glcp-(1-->4)-beta-Manp-(1-->4)-Man, and beta-Manp-(1-->4)-[alpha-Galp-(1-->6)]-Man, consistent with a backbone containing alternating -->4)-beta-Manp-(1--> and -->4)-beta-Glcp-(1--> residues in a approximately 15:1 ratio. Analysis of the sample treated sequentially with endo-(1-->4)-beta-d-mannanase and alpha-D-galactosidase showed that the majority of alpha-Galp-(1--> residues were linked to O-2, O-3, or O-6 of -->4)-beta-Manp-(1--> residues, with approximately 16 -->4)-beta-Manp-(1--> residues between side chains. Our data provide direct evidence of a previously proposed glucomannan backbone, but draw into question previously proposed side-chain structures.
Tai-Nin Chow
Jimmy
J
Department of Chemistry, The University of Texas at Dallas, PO Box 830688, Richardson, TX 75083-0688, USA.
Williamson
David A
DA
Yates
Kenneth M
KM
Goux
Warren J
WJ
D000504:Aloe / Q000737:chemistry* / Q000276:immunology*; D002240:Carbohydrate Sequence; D006868:Hydrolysis; D007155:Immunologic Factors / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D011134:Polysaccharides / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D012995:Solubility; D014867:Water
D007155:Immunologic Factors; D011134:Polysaccharides; D014867:Water