Characteristics of xyloglucan after attack by hydroxyl radicals

Carbohydr Res. 2001 Jun 15;332(4):389-403. doi: 10.1016/s0008-6215(01)00110-0.

Abstract

It has been proposed that plant cell-wall polysaccharides are subject in vivo to non-enzymic scission mediated by hydroxyl radicals (-*OH). In the present study, xyloglucan was subjected in vitro to partial, non-enzymic scission by treatment with ascorbate plus H(2)O(2), which together generate -*OH. The partially degraded xyloglucan appeared to contain ester bonds within the backbone, as indicated by an irreversible decrease in viscosity upon alkaline hydrolysis. Aldehyde and/or ketone groups were also introduced into the polysaccharide by -*OH-attack, as indicated by staining with aniline hydrogen-phthalate and by reaction with NaB(3)H(4). The introduction of ester and oxo groups supports the proposed sequence of reactions: (a) -*OH-mediated H-abstraction to produce a carbon-centred carbohydrate radical; (b) reaction of the latter with O(2); and (c) elimination of a hydroperoxyl radical (HO(2)*-). When the partially degraded xyloglucan was reduced with NaB(3)H(4) followed by acid hydrolysis, several 3H-aldoses were detected ([3H]galactose, [3H]xylose, [3H]glucose, [3H]ribose and probably [3H]mannose), in addition to unidentified 3H-products (probably including anhydroaldoses). 3H-Alditols were undetectable, showing that few or no conventional reducing termini were introduced. Digestion of the NaB(3)H(4)-reduced, partially degraded xyloglucan with Driselase released 25 times more [3H]Xyl-alpha-(1-->6)-Glc than Xyl-alpha-(1-->6)-[3H]Glc, suggesting that the xylose side-chains of the xyloglucan had been more heavily attacked by -*OH than the glucose residues of the backbone. The radioactive xyloglucan was readily digested by cellulase, yielding 3H-products in the hepta- to nonasaccharide range. A fingerprinting strategy for identifying -*OH-attacked xyloglucan in plant cell walls is proposed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ascorbic Acid
  • Borohydrides
  • Carbohydrate Conformation
  • Carbohydrate Sequence
  • Fabaceae / chemistry
  • Galactose / analysis
  • Glucans*
  • Glucose / analysis
  • Hydrogen Peroxide
  • Hydroxyl Radical*
  • Mannose / analysis
  • Molecular Sequence Data
  • Oligodeoxyribonucleotides / chemistry
  • Plants, Medicinal
  • Polysaccharides / chemistry*
  • Ribose / analysis
  • Seeds / chemistry
  • Tritium
  • Xylans*
  • Xylose / analysis

Substances

  • Borohydrides
  • Glucans
  • Oligodeoxyribonucleotides
  • Polysaccharides
  • Xylans
  • Tritium
  • Hydroxyl Radical
  • xyloglucan
  • Ribose
  • sodium borohydride
  • Xylose
  • Hydrogen Peroxide
  • Glucose
  • Mannose
  • Ascorbic Acid
  • Galactose