Characterisation of aphid myrosinase and degradation studies of glucosinolates

Authors

  • Frédéric Francis,

    Corresponding author
    1. Department of Pure and Applied Zoology, Gembloux Agricultural University, Passage des Déportés 2, Gembloux, Belgium
    • Department of Pure and Applied Zoology, Gembloux Agricultural University, Passage des Déportés 2, B5030 Gembloux, Belgium
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  • Georges Lognay,

    1. Department of General and Organic Chemistry, Gembloux Agricultural University, Passage des Déportés 2, Gembloux, Belgium
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  • Jean-Paul Wathelet,

    1. Department of General and Organic Chemistry, Gembloux Agricultural University, Passage des Déportés 2, Gembloux, Belgium
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  • Eric Haubruge

    1. Department of Pure and Applied Zoology, Gembloux Agricultural University, Passage des Déportés 2, Gembloux, Belgium
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Abstract

Myrosinase from Brevicoryne brassicae was purified by ammonium sulfate fractionation, dialysis, and chromatography on a DEAE column. The chromatography yielded a single peak and a 115.6-fold purification. Further FPLC gel filtration gave a single peak at 120 kDa. Denaturing SDS/PAGE of the protein revealed a single band at 60 kDa, indicating that the native B. brassicae myrosinase is a dimer. Kinetic parameters towards 8 glucosinolates were calculated. Strong differences of Vmax and Km were observed depending on the substrate. Degradation products of each glucosinolate were identified and quantified by GC-MS and GLC-FID, respectively. Using both crude aphid homogenates and purified myrosinase, two unique hydroxyglucosinolates, 3-butenyl- and benzyl-isothiocyanates were identified from progoitrin ((2S)-2-hydroxybut-3-enyl-glucosinolate) and sinalbin (4-hydroxybenzyl-glucosinolate) degradation respectively. Addition of ascorbic acid to the reaction mixtures containing sinalbin and progoitrin caused the production of hydroxylated degradation products usually associated with plant myrosinase metabolisation. The occurrence of the myrosinase system in B. brassicae is discussed in terms of similar allelochemical adaptation between the herbivore and its host plant. Arch. Insect Biochem. Physiol. 50:173–182, 2002. © 2002 Wiley-Liss, Inc.

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