POTATO XYLOGLUCAN IS BUILT FROM XXGG-TYPE SUBUNITS

Extraction of potato cell-wall material with solutions of increasing s trength of alkali yielded a xyloglucan-rich fraction which was further purified by anion-exchange chromatography and treatment with alpha-am ylase and endogalactanase. Methylation analysis indicated that the pur ified xyloglucan contained a high percentage of unsubstituted glucosyl residues compared to, for instance, apple xyloglucan, and equal amoun ts of Xyl-(1 --> 6)-, Gal-(1 --> 2)-Xyl-(1 --> 6)-, and Ara-(1 --> 2)- Xyl-(1 --> 6)-sidechains. This xyloglucan was degraded with endoglucan ase (endoV), purified from Trichoderma viride. The resulting digest wa s fractionated by BioGel P-2 chromatography, followed by preparative h igh-performance anion-exchange chromatography of the pentamer to nonam er fractions. The purified oligosaccharides were characterized by mono saccharide analysis, mass spectrometry, and degradation with an exoglu canase. Degradation of potato xyloglucan by another endoglucanase (end oIV) of Trichoderma viride yielded a different set of products. EndoIV released predominantly oligosaccharides with two unbranched glucosyl residues at the reducing terminus, whereas endoV also released product s containing unbranched glucosyl residues on both ends of the molecule . A difference in the mode of action of endoglucanases with xyloglucan -degrading activity is demonstrated. (C) 1996 Elsevier Science Ltd.