Feruloylated Arabinoxylans Are Oxidatively Cross- Linked by Extracellular Maize Peroxidase but Not by Horseradish Peroxidase  

作　　者：Sally J. Burr Stephen C. Fry 

机构地区：[1]The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, School of Biological Sciences, The University of Edinburgh, Daniel Rutherford Building, The King's Buildings, Edinburgh EH9 3JH, UK [2]Present address: Ecologie Microbienne/UMR CNRS 5557 USC INRA 1193, Universite Claude Bernard--Lyon 1, Batiment Gregor Mendel, 16 rue Dubois, F-69622 Villeurbanne Cedex, France

出　　处：《Molecular Plant》2009年第5期883-892,共10页分子植物（英文版）

摘　　要：Covalent cross-linking of soluble extracellular arabinoxylans in living maize cultures, which models the cross- linking of wall-bound arabinoxylans, is due to oxidation of feruloyl esters to oligoferuloyl esters and ethers. The oxidizing system responsible could be H2O2/peroxidase, O2/laccase, or reactive oxygen species acting non-enzymically, To distinguish these possibilities, we studied arabinoxylan cross-linking in vivo and in vitro. In living cultures, exogenous, soluble, extracellular, feruloylated [pentosyl-3H]arabinoxylans underwent cross-linking, beginning abruptly 8 d after sub-culture. Crosslinking was suppressed by iodide, an H2O2 scavenger, indicating dependence on endogenous H2O2. However, exogenous H2O2 did not cause precocious cross-linking, despite the constant presence of endogenous peroxidases, suggesting that younger cultures contained natural cross-linking inhibitors. Dialysed culture-filtrates cross-linked [^3H]arabinoxylans in vitro only if H2O2 was also added, indicating a peroxidase requirement. This cross-linking was highly ionic-strength-dependent. The peroxidases responsible were heat-labile, although relatively heat-stable peroxidases （assayed on o-dianisidine） were also present. Surprisingly, added horseradish peroxidase, even after heat-denaturation, blocked the arabinoxylancross-linking action of maize peroxidases, suggesting that the horseradish protein was a competing substrate for [^3H]arabinoxylan coupling. In conclusion, we show for the first time that cross-linking of extracellular arabinoxylan in living maize cultures is an action of apoplastic peroxidases, some of whose unusual properties we report.Covalent cross-linking of soluble extracellular arabinoxylans in living maize cultures, which models the cross- linking of wall-bound arabinoxylans, is due to oxidation of feruloyl esters to oligoferuloyl esters and ethers. The oxidizing system responsible could be H2O2/peroxidase, O2/laccase, or reactive oxygen species acting non-enzymically, To distinguish these possibilities, we studied arabinoxylan cross-linking in vivo and in vitro. In living cultures, exogenous, soluble, extracellular, feruloylated [pentosyl-3H]arabinoxylans underwent cross-linking, beginning abruptly 8 d after sub-culture. Crosslinking was suppressed by iodide, an H2O2 scavenger, indicating dependence on endogenous H2O2. However, exogenous H2O2 did not cause precocious cross-linking, despite the constant presence of endogenous peroxidases, suggesting that younger cultures contained natural cross-linking inhibitors. Dialysed culture-filtrates cross-linked [^3H]arabinoxylans in vitro only if H2O2 was also added, indicating a peroxidase requirement. This cross-linking was highly ionic-strength-dependent. The peroxidases responsible were heat-labile, although relatively heat-stable peroxidases （assayed on o-dianisidine） were also present. Surprisingly, added horseradish peroxidase, even after heat-denaturation, blocked the arabinoxylancross-linking action of maize peroxidases, suggesting that the horseradish protein was a competing substrate for [^3H]arabinoxylan coupling. In conclusion, we show for the first time that cross-linking of extracellular arabinoxylan in living maize cultures is an action of apoplastic peroxidases, some of whose unusual properties we report.

关 键 词：Cell wall CROSS-LINKS phenolics FERULATE PEROXIDASE soluble extracellular polysaccharides Zea mays L. 

分 类 号：Q554.6[生物学—生物化学] TS262.5[轻工技术与工程—发酵工程]