Structure elucidation of an immunostimulatory arabinoxylan-type polysaccharide prepared from young barley leaves (Hordeum vulgare L.).

We recently isolated an immunostimulating polysaccharide (BLE-P-I), which possesses a large proportion of arabinoxylan, from young barley leaves. In the present study, to elucidate the structural details of BLE-P-I, it was fractionated into enzyme-resistant fraction (BLE-P-I-X1) and arabinoxylan-rich oligosaccharide fraction (BLE-P-I-X2) after endo-xylanase hydrolysis. Commercial wheat arabinoxylan was also fractionated into WAX-XI and WAX-X2 after the same treatment. BLE-P-I-X2 consisted of arabinose and xylose, including 11 types of neutral glycosidic linkages, whereas WAX-X2 had less, with 6 types of linkages. Mass spectrometric results indicated that WAX-X2 was composed of a xylan backbone bearing only arabinose. In contrast, BLE-P-I-X2 consisted of a xylan backbone with acetate, arabinose, galactose, glucuronic acid, and 4-O-methylglucuronic acid, resembling structural characteristics as glucuronoarabinoxylan. Macrophage-stimulatory activity showed that BLE-P-I-X2 has a role in the expression of the activity. These results indicate that the structural complexity of arabinoxylan seems to be responsible for the immunomodulatory activity in barley leaf.