Composition and structure of a galactomannan macromolecule from seeds ofAstragalus lehmannianus bunge

• Published in: Applied biochemistry and microbiology Vol. 36; no. 5; pp. 502 - 506
• Main Authors: Mestechkina, N M, Anulov, O V, Smirnova, N I, Shcherbukhin, V D
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01.09.2000
• Subjects: Aqueous solutions; Astragalus lehmannianus; Chains; Composition; D-Galactose; Endemic species; Galactose; Infrared spectroscopy; Legumes; Magnetic resonance spectroscopy; Mannose; Molecular weight; NMR; NMR spectroscopy; Nuclear magnetic resonance; Optical activity; Rotation; Seeds; Spectrum analysis
• ISSN: 0003-6838; 1608-3024
• DOI: 10.1007/BF02731898

The composition and structure of a galactomannan from seeds ofAstragalus lehmannianus, an endemic legume species, is reported for the first time. The purified galactomannan (yield, 4.8%) contained 55% D-mannose and 45%D-galactose and had a molecular weight of 997.03 kDa. Its aqueous solutions were optically active and highly viscous (the specific rotation [α]D equaled +81.3°; the characteristic viscosity [η], 868.4 ml/g). Chemical, Chromatographic, and spectral (IR and13C-NMR spectroscopy) methods were used to demonstrate that the main chain of the molecule is formed by residues of 1,4-β-D-mannopyranose, 78% of which are substituted at position 6 with single α-D-galactopyranose. The distribution of galactose along the chain was calculated from NMR spectra: frequencies of occurrence per pair of neighboring mannose units of ( 1 ) two substituents, (2) one substituent, and (3) no substituents were 65.3%, 31.5, and 3.2, respectively. The specific rotation of the galactomannans was shown to correlate with their content of galactose.