Isolation and partial characterization of three isoamylases of Rhyzopertha dominica F. (Coleoptera: Bostrichidae)

Structural features, substrate specificity, kinetic properties of insect α-amylase and specificity of plant α-amylase inhibitors

BACKGROUND

α-Amylase is an important digestive enzyme required for the optimal growth and development of insects. Several insect α-amylases had been purified and their physical and chemical properties were characterized. Insect α-amylases of different orders display variability in structure, properties and substrate specificity. Such diverse properties of amylases could be due to different feeding habits and gut environment of insects.

KEY POINTS

In this review, structural features and properties of several insect α-amylases were compared. This could be helpful in exploring the diversity in characteristics of α-amylase between the members of the same class (insecta). Properties like pH optima are reflected in enzyme structural features. In plants, α-amylase inhibitors (α-AIs) occur as part of natural defense mechanisms against pests by interfering in their digestion process and thus could also provide access to new pest management strategies. AIs are quite specific in their action; therefore, these could be employed according to their effectiveness against target amylases. Potential of transgenics with α-AIs has also been discussed for insect resistance and controlling infestation.

CONCLUSIONS

The differences in structural features of insect α-amylases provided reasons for their efficient functioning at different pH and the specificity towards various substrates. Various proteinaceous and non-proteinaceous inhibitors discussed could be helpful in controlling pest infestation. In depth detailed studies are required on proteinaceous α-AI-α-amylase interaction at different pH's as well as the insect proteinase action on these inhibitors before selecting the α-AI for making transgenics resistant to particular insect.

Modified alpha-amylase activity among insecticide-resistant and -susceptible strains of the maize weevil, Sitophilus zeamais

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.

Purification and characterization of an organic-solvent-tolerant halophilic α-amylase from the moderately halophilic Nesterenkonia sp. strain F

A halophilic α-amylase produced by Nesterenkonia sp. strain F was purified to homogeneity by 80% ethanol precipitation, Q-Sepharose anion exchange, and Sephacryl S-200 gel filtration chromatography. The purified amylase exhibited specific activity of 357 unit/mg protein that corresponds to twofold purification. The molecular mass of the amylase was determined to be 57 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and gel filtration chromatography. The optimal pH and temperature for enzyme activity were 6.5 and 45°C, respectively. The amylase was active over a wide range of salt concentrations (0-4 M) with maximum activity at 0.75-1 M NaCl. The α-amylase activity was stimulated by Ca(2+) and inhibited by ethylenediamine tetraacetic acid (EDTA), suggesting that this enzyme is a metalloenzyme. The purified enzyme showed remarkable stability towards surfactants (Tween 20, Tween 80, and Triton X-100), and its activity was increased by β-mercaptoethanol. The halophilic α-amylase was stable in the presence of various organic solvents such as benzene, chloroform, toluene, and cyclohexane. These properties indicate wide potential applications of this α-amylase in starch-processing industries.