title: Fungal auxin antagonist hypaphorine competitively inhibits indole-3-acetic acid-dependent superoxide generation by horseradish peroxidase.
abstract: Plant peroxidases (EC 1.11.1.7) including horseradish peroxidase (HRP-C), but not the nonplant peroxidases, are known to be highly specific indole-3-acetic acid (IAA) oxygenases which oxidize IAA in the absence of H2O2, and superoxide anion radicals (O2*-) are produced as by-products. Hypaphorine, a putative auxin antagonist isolated from ectomycorrhizal fungi, inhibited the IAA-dependent generation of O2*- by HRP-C, which occurs in the absence of H2O2. Hypaphorine has no effect on the nonspecific heme-catalyzed O2*- generation induced by high concentration of ethanol. It is probable that the inhibitory effect of hypaphorine on O2*- generation is highly specific to the IAA-dependent reaction. The mode of inhibition of the IAA-dependent O2*--generating reaction by hypaphorine was analyzed with a double-reciprocal plot and determined to be competitive inhibition, indicating that hypaphorine competes with IAA by binding to the putative IAA binding site on HRP-C. This implies the importance of structural similarity between hypaphorine and IAA. This work presented the first evidence for antagonism between IAA and a structurally related fungal alkaloid on binding to a purified protein which shares some structural similarity with auxin-binding proteins.
authors.affiliation: Unité Mixte de Recherche INRA-UHP Interactions Arbres/Micro-organismes, Institut National de la Recherche Agronomique, Champenoux, F-54280, France.
authors.forename: T
authors.initials: T
authors.lastname: Kawano
authors.forename: N
authors.initials: N
authors.lastname: Kawano
authors.forename: H
authors.initials: H
authors.lastname: Hosoya
authors.forename: F
authors.initials: F
authors.lastname: Lapeyrie
mesh_terms: D001667:Binding, Competitive; D005658:Fungi / Q000737:chemistry; D006735:Horseradish Peroxidase / Q000378:metabolism*; D007210:Indoleacetic Acids / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology*; D008163:Luminescent Measurements; D009195:Peroxidase / Q000378:metabolism; D010944:Plants / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D016897:Respiratory Burst / Q000187:drug effects; D012997:Solvents / Q000737:chemistry; D013481:Superoxides / Q000378:metabolism*
chemical_list: D007210:Indoleacetic Acids; D007211:Indoles; D017382:Reactive Oxygen Species; D012997:Solvents; D013481:Superoxides; C030737:indoleacetic acid; D006735:Horseradish Peroxidase; D009195:Peroxidase; C001529:lenticin