Abstract
The production of an extracellular β-glucosidase by Aspergillus niger NRRL 599 was optimized using submerged fermentation technique. Effect of different media, different carbon sources, initial pH of the fermentation medium, temperature, incubation period and inoculum size on the production of β- glucosidase enzyme was investigated. A. niger NRRL 599 produced maximum extracellular β- glucosidase (4.48 U/mg) in Eggins and Pugh medium with 1% wheat bran (w/v) at pH 5.5 inoculated with 4% conidial suspension after 96 h of incubation at 30°C. Purified β-glucosidase gave K m and V max values of 3.11 mM and 20.83 U/mg respectively for pNPG hydrolysis. The enzyme was optimally active at pH 4.8 and at temperature of 60°C. Thermodynamic parameters, E a , ΔH and ΔS were found to be 52.17 KJ/mol, 49.90 J/mol.K and -71.69 KJ/mol, respectively. The pKa1 and pKa 2 of ionizable groups of active site residues involved in V max were calculated to be 4.1 and 6.0 respectively. Key words : β-Glucosidase, Aspergillus niger, kinetics, thermodynamics.
Highlights
A. niger NRRL 599 produced maximum extracellular βglucosidase (4.48 U/mg) in Eggins and Pugh medium with 1% wheat bran (w/v) at phosphate buffer (pH) 5.5 inoculated with 4% conidial suspension after 96 h of incubation at 30°C
Β-Glucosidase (EC 3.2.1.21) catalyzes the hydrolysis of β-1,4 glucosidic bonds in disaccharides, oligosaccharides, alkyl and aryl β-D-glucosides by attacking on the non-reducing terminal and releases β-D glucose (Iwashita et al, 1999; Wallecha and Mishra, 2003). β-Glucosidase is produced by humans, insects, plants, bacteria, fungi and yeast (Villena et al, 2007)
Responsible for the regulation of the whole cellulolytic process and is a rate-limiting factor during enzymatic hydrolysis of cellulose, as both endoglucanase and exoglucanase activities are often inhibited by cellobiose
Summary
Β-Glucosidase (EC 3.2.1.21) catalyzes the hydrolysis of β-1,4 glucosidic bonds in disaccharides, oligosaccharides, alkyl and aryl β-D-glucosides by attacking on the non-reducing terminal and releases β-D glucose (Iwashita et al, 1999; Wallecha and Mishra, 2003). β-Glucosidase is produced by humans, insects, plants, bacteria, fungi and yeast (Villena et al, 2007). The production of an extracellular β-glucosidase by Aspergillus niger NRRL 599 was optimized using submerged fermentation technique. Different carbon sources, initial pH of the fermentation medium, temperature, incubation period and inoculum size on the production of βglucosidase enzyme was investigated.
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