ESR study of the non-enzymic scission of xyloglucan by an ascorbate-H2O2-copper system: the involvement of the hydroxyl radical and the degradation of ascorbate.
Xyloglucan is degraded by a mixture of copper(II), hydrogen peroxide and ascorbate. In the presence of ascorbate and/or hydrogen peroxide, copper(II) species were rapidly reduced to copper(I), which react with hydrogen peroxide. Spin-trapping experiments showed that hydroxyl radicals formed and attacked xyloglucan causing its degradation. The formation of a carbon-centred ascorbyl (C-ascorbyl) radical and its degradation with the formation of oxalate, was also caused by hydroxyl radicals. As a consequence, the features of the bis(oxalate) copper(II) complex clearly appeared in the frozen solution ESR spectra. The formation of carbon-centred radicals on the xyloglucan is the trigger for a series of possible molecular rearrangements which led to its oxidative scission.
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Istituto per lo Studio delle Sostanze Naturali di Interesse Alimentare e Chimico-Farmaceutico, CNR, Sezione per lo Studio dei Metalloenzimi, Catania, Italy.
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D001205:Ascorbic Acid / Q000378:metabolism*; D003300:Copper / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005936:Glucans; D006861:Hydrogen Peroxide / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry* / Q000378:metabolism; D014990:Xylans
D005936:Glucans; D011134:Polysaccharides; D014990:Xylans; C029353:xyloglucan; D003300:Copper; D006861:Hydrogen Peroxide; D001205:Ascorbic Acid