title: Modified alpha-amylase activity among insecticide-resistant and -susceptible strains of the maize weevil, Sitophilus zeamais.
abstract: Fitness cost is usually associated with insecticide resistance and may be mitigated by increased energy accumulation and mobilization. Preliminary evidence in the maize weevil (Coleoptera: Curculionidae) suggested possible involvement of amylases in such phenomenon. Therefore, alpha-amylases were purified from an insecticide-susceptible and two insecticide-resistant strains (one with fitness cost [resistant cost strain], and the other without it [resistant no-cost strain]). The main alpha-amylase of each strain was purified by glycogen precipitation and ion-exchange chromatography (>or=70-fold purification, <or=19% yield). Single alpha-amylase bands with the same molecular mass (53.7kDa) were revealed for each insect strain. Higher activity was obtained at 35-40 degrees C and at pH 5.0-7.0 for all of the strains. The alpha-amylase from the resistant no-cost strain exhibited higher activity towards starch and lower inhibition by acarbose and wheat amylase inhibitors. Opposite results were observed for the alpha-amylase from the resistant cost strain. Although the alpha-amylase from the resistant cost strain exhibited higher affinity to starch (i.e., lower K(m)), its V(max)-value was the lowest among the strains, particularly the resistant no-cost strain. Such results provide support for the hypothesis that enhanced alpha-amylase activity may be playing a major role in mitigating fitness costs associated with insecticide resistance.
authors.affiliation: Departamento de Bioquímica e Biologia Molecular, Instituto de Biotecnologia Aplicada à Agropecuária (BIOAGRO), Universidade Federal de Viçosa, Viçosa, MG, Brazil.
authors.forename: K V G
authors.initials: KV
authors.lastname: Lopes
authors.forename: L B
authors.initials: LB
authors.lastname: Silva
authors.forename: A P
authors.initials: AP
authors.lastname: Reis
authors.forename: M G A
authors.initials: MG
authors.lastname: Oliveira
authors.forename: R N C
authors.initials: RN
authors.lastname: Guedes
mesh_terms: D020909:Acarbose; D000704:Analysis of Variance; D000818:Animals; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D056084:Genetic Fitness / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007305:Insecticide Resistance / Q000502:physiology*; D007700:Kinetics; D013213:Starch / Q000378:metabolism; D013379:Substrate Specificity; D013696:Temperature; D048889:Weevils / Q000201:enzymology* / Q000235:genetics; D000516:alpha-Amylases / Q000378:metabolism*
chemical_list: D013213:Starch; D000516:alpha-Amylases; D020909:Acarbose