Structural studies of the carbohydrate moieties of lectins from potato (Solanum tuberosum) tubers and thorn-apple (Datura stramonium) seeds

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Abstract
Methylation analysis of potato (S. tuberosum) lectin and thorn-apple (D. stramonium) lectin confirmed previous conclusions that both glycoproteins contained high proportions of L-arabinofuranosides and lesser amounts of D-galactopyranosides. The arabinofuranosides are present in both lectins as short unbranched chains containing 1 .fwdarw. 2- and 1 .fwdarw. 3-linkages, which are linked to hydroxyproline. Galactopyranosides are present as monosaccharides, which are attached to serine, in potato lectin and as both the monosaccharide and the 1 .fwdarw. 3-linked disaccharide in Datura lectin. Alkaline digestion of potato lectin and subsequent separation of the components by gel filtration led to the isolation of 4 fractions corresponding to the mono-, di-, tri- and tetra-arabinosides of hydroxyproline. The latter 2 fractions accounted for > 70% of the total hydroxyproline. Methylation analysis showed that the triarabinoside contained only 1 .fwdarw. 2-linkages between sugars, but the tetra-arabinoside contained both 1 .fwdarw. 2- and 1 .fwdarw. 3-linkages. Direct-insertion mass spectrometry of these compounds using electron impact and chemical ionization, in a comparison with other known structural patterns, was used to determine the sequences of the sugars.