Structures of aldouronic acids liberated from kenaf xylan by endoxylanases from Streptomyces sp.

Streptomyces sp. SK519 was cultivated in the medium containing 0.5% birch wood xylan to produce extracellular xylanase. The xylanase was isolated from the culture supernatant by ammonium sulfate precipitation and partially purified by absorbing on the insoluble xylan. Alkali-extracted kenaf glucuronoylan of which main chain primarily consisting of (1-4)-linked β-D-xylopyranose (Xylp), some of which carry α-(1-2)-linked 4-O-methylglucopyranosyl acid (MeGlcAp) and glucopyranosyluronic acid (GlcAp) as side chain was digested with the xylanase preparation. At the final stage of digestion, main neutral oligosaccharides were xylotriose (Xyl3) and xylobiose (Xyl2) followed by xylotetraose (Xyl4). Xylose was only formed in a trace amount. As acidic oligosaccharides liberated, following seven aldopentao- and aldotetraouronic acids were isolated in a pure state, respectively, by preparative anion-exchange chromatography. Their structures were determined by analysis of constitutional sugar residues and 1H and 13C NMR spectroscopy. 1,4-[MeGlcA-α-1,2-]Xyl-β-1,4-Xyl-β-1,4-Xyl; A-α-1,2-]Xyl-β-1,4-Xyl-β-1,4-Xyl-β-1,4-Xyl; 1,4-[GlcA-α-1,2-]Xyl-β-1,4-Xyl-β-1,4-Xyl α-1,2-]Xyl-β-1,4-Xyl-β-1,4-Xyl-β-1,4-Xyl A-α-1,2-]Xyl-β-1,4-Xyl-β-1,4-D-Xyl α-1,2-]Xyl-β-1,4-Xyl-β-1,4-Xyl 1,4-Xyl-β-1,3-Rha-α-1,2-GalA-α-1,4-Xyl