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Chemical modification results in hyperactivation and thermostabilization of Fusarium solani glucoamylase

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Chemical modification of carboxyl groups of glucoamylase from a mesophilic fungus, Fusarium solani, was carried out using ethylenediamine as nucleophile in the presence of water-soluble 1-ethyl-3(3-dimethylaminopropyl)carbodiimide. Modification brought about a dramatic enhancement of catalytic activity and thermal stability of glucoamylase. Temperature and pH optima of ethylenediamine-coupled glucoamylase (ECG) increased as compared with those of native enzyme. The specificity constant (kcat/Km) of native, ECG-2, ECG-11, and ECG-17 was 136, 173, 225, and 170, respectively, at 55 °C. The enthalpy of activation (ΔH*) and free energy of activation (ΔG*) for soluble starch hydrolysis were lower for the chemically modified forms. All of the modified forms werestable at higher temperatures and possessed high ΔG* against thermal unfolding. The effects of α-chymotrypsin and subtilisin on the modified forms were activating as compared with native. Moreover, denaturation of ECG-2, ECG-11, and ECG-17 in urea at 4 mol·L–1 also showed an activation trend. A possible explanation for the thermal denaturation of native and increased thermal stability of ECG-2, ECG-11, and ECG-17 at higher temperatures is also discussed.

La modification chimique des groupes carboxyles de la glucoamylase du champignon mésophile Fusarium solani a été réalisée à l’aide d’éthylène-diamine comme nucléophile, en présence du 1-éthyl-3(3-diméthylaminopropyl)carbodiimide hydrosoluble. La modification a résulté en une forte augmentation de l’activité catalytique et de la stabilité thermique de la glucoamylase. La température et le pH optimaux de la glucoamylase couplée à l’éthylène-diamine (ECG) étaient plus élevés, comparativement à l’enzyme native. La constante de spécificité (kcat/Km) de l’enzyme native et des dérivés ECG-2, ECG-11 et ECG-17 était de 136, 173, 225 et 170 respectivement à 55 °C. L’enthalpie d’activation (ΔH*) et l’énergie libre d’activation (ΔG*) de l’hydrolyse d’amidon soluble étaient plus faibles chez les formes modifiées. Toutes les formes modifiées étaient thermiquement stables à des températures plus élevées et possédaient une haute ΔG* envers le dépliement thermique. Les effets de l’α-chymotrypsine et de la subtilisine sur les formes modifiées comparativement à la forme native étaient activateurs. De plus, la dénaturation de ECG-2, ECG-11 et ECG-17 dans l’urée 4 mol·L–1 tendait aussi vers l’activation. Une explication possible de la dénaturation thermique de la forme native et de la stabilité thermique des formes ECG-2, ECG-11 et ECG-17 à plus haute température est aussi discutée.

Document Type: Research Article

Publication date: 2007-02-01

More about this publication?
  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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