The biochemical basis for L-canavanine tolerance by the tobacco budworm Heliothis virescens (Noctuidae).
The tobacco budworm, Heliothis virescens (Noctuidae), a destructive insect pest, is remarkably resistant to L-canavanine, L-2-amino-4-(guanidinooxy)butyric acid, an arginine antimetabolite that is a potent insecticide for nonadapted species. H. virescens employs a constitutive enzyme of the larval gut, known trivially as canavanine hydrolase (CH), to catalyze an irreversible hydrolysis of L-canavanine to L-homoserine and hydroxyguanidine. As such, it represents a new type of hydrolase, one acting on oxygen-nitrogen bonds (EC 3.13.1.1). This enzyme has been isolated from the excised gut of H. virescens and purified to homogeneity; it exhibits an apparent Km value for L-canavanine of 1.1 mM and a turnover number of 21.1 micromol x min(-1)x micromol(-1). This enzyme has a mass of 285 kDa and is composed of two subunits with a mass of 50 kDa or 47.5 kDa. CH has a high degree of specificity for L-canavanine as it cannot function effectively with either L-2-amino-5-(guanidinooxy)pentanoate or L-2-amino-3-(guanidinooxy)propionate, the higher or lower homolog of L-canavanine, respectively. L-Canavanine derivatives such as methyl-L-canavanine, or L-canaline and O-ureido-L-homoserine, are not metabolized significantly by CH.
Melangeli
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Universidad Central de Venezuela, Centro de Bioquimica Nutricional, Maracay, Venezuela.
Rosenthal
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GA
Dalman
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DL
D000096:Acetone; D000595:Amino Acid Sequence; D000645:Ammonium Sulfate; D000818:Animals; D002172:Canavanine / Q000378:metabolism* / Q000633:toxicity*; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D004064:Digestive System / Q000201:enzymology; D006146:Guanidines / Q000378:metabolism; D006714:Homoserine / Q000378:metabolism; D006867:Hydrolases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006898:Hydroxylamines; D007305:Insecticide Resistance; D007306:Insecticides / Q000633:toxicity*; D007700:Kinetics; D007814:Larva; D008969:Molecular Sequence Data; D009036:Moths / Q000201:enzymology / Q000502:physiology*; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification
D006146:Guanidines; D006898:Hydroxylamines; D007306:Insecticides; D010446:Peptide Fragments; D000096:Acetone; D002172:Canavanine; D006714:Homoserine; C029604:hydroxyguanidine; D006867:Hydrolases; C105155:canavanine hydrolase; D000645:Ammonium Sulfate