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Purification and thermodynamic characterization of glucose oxidase from a newly isolated strain of Aspergillus niger

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Abstract:

An intracellular glucose oxidase (GOD) was isolated from the mycelium extract of a locally isolated strain of Aspergillus niger NFCCP. The enzyme was partially purified to a yield of 28.43% and specific activity of 135 U mg–1 through ammonium sulfate precipitation, anion-exchange chromatography, and gel filtration. The enzyme showed high specificity for D-glucose, with a Km value of 25 mmol L–1. The enzyme exhibited optimum catalytic activity at pH 5.5. Optimum temperature for GOD-catalyzed D-glucose oxidation was 40 °C. The enzyme displayed a high thermostability having a half-life (t1/2) of 30 min, enthalpy of denaturation (H*) of 99.66 kJ mol–1, and free energy of denaturation (G*) of 103.63 kJ mol–1. These characteristics suggest that GOD from A. niger NFCCP can be used as an analytical reagent and in the design of biosensors for clinical, biochemical, and diagnostic assays.Key words: glucose oxidase, Aspergillus niger, kinetics, thermodynamics, thermal stability.

Une glucose oxydase (GOD) extracellulaire fut isolée de l'extrait du mycélium d'une souche isolée localement de Aspergillus niger NFCCP. L'enzyme fut partiellement purifiée avec un rendement de 28,43 % et une activité spécifique de 135 U mg–1 par précipitation au sulfate d'ammonium, chromatographie à échange anionique et filtration sur gel. L'enzyme a démontré une spécificité élevée au D-glucose, avec une valeur Km de 25 mmol L–1. L'enzyme a démontré une activité catalytique optimale à un pH de 5,5. La température optimale pour l'oxydation du D-glucose catalysée par la GOD était de 40 °C. L'enzyme a manifesté une thermostabilité élevée avec une demi-vie (t1/2) de 30 min, une enthalpie de dénaturation (H*) de 99,66 kJ mol–1 est une énergie libre de dénaturation (G*) de 103,63 kJ mol–1. Ces caractéristiques encouragent l'utilisation de la GOD de A. niger NFCCP comme réactif analytique et dans la conception des biosenseurs pour des analyses cliniques, biochimiques et diagnostiques.Mots clés : glucose oxydase, Aspergillus niger, cinétique, thermodynamique, stabilité thermique.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: June 1, 2006

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  • 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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