Production of cellulases by Aspergillus fumigatus and characterization of one beta-glucosidase

Aspergillus fumigatus produces substantial extracellular cellulases on several cellulosic substrates including simple sugars. Low glucose potentiates enzyme production, but most cellulose-induced cellulases are repressed by high glucose. As production of cellulase in a wide substrate range is unusua...

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Veröffentlicht in:Current microbiology 1996-03, Vol.32 (3), p.119-123
Hauptverfasser: Ximenes, E.A. (Universidade de Brasilia, Brasilia, Brasil.), Felix, C.R, Ulhoa, C.J
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Sprache:eng
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Zusammenfassung:Aspergillus fumigatus produces substantial extracellular cellulases on several cellulosic substrates including simple sugars. Low glucose potentiates enzyme production, but most cellulose-induced cellulases are repressed by high glucose. As production of cellulase in a wide substrate range is unusual, the cellulolytic complex of this thermophilic fungus was investigated. A beta-glucosidase was separated by gel filtration and ion-exchange chromatography. It migrated in native polyacrylamide gel as a single protein (130 kDa), which split under denaturing conditions into two smaller proteins having molecular masses of 90 kDa and 45 kDa. However, only the 90-kDa protein was active. Conventional chromatographic procedures were unsuccessful for the separation of these two proteins. Therefore, the 130-kDa protein was studied for its kinetic properties. It hydrolyzed p-nitrophenyl-beta-D-glucopyranoside (p-NPG) and cellobiose, but not beta-glucans, laminarin, and p-nitrophenyl-beta-D-xilopyranoside. The optimal pH and temperature of p-NPG and cellobiose hydrolysis were 5.0 and 4.0, and 65 degrees C and 60 degrees C, respectively. The Km values, determined for cellobiose and p-NPG of hydrolysis, were 0.075 mM and 1.36 mM, respectively. Glucose competitively inhibited the hydrolysis of p-NPG. The Ki was 3.5 mM
ISSN:0343-8651
1432-0991
DOI:10.1007/s002849900021