Production and characterization of a thermostable extracellular esterase from Aspergillus niger

A strain of Aspergillus niger NRRL 337 degrade agro-industrial waste i.e wheat bran in solid state fermentation and produce esterase enzyme. Maximum enzyme activity 15.2 U/ml was produced after 72 h of incubation at 30 degrees C. The protein was partially purified by performing ammonium sulfate precipitation and immobilized metal ion chromatography (IMAC) technique. SDS-PAGE analysis showed molecular weight of esterase was 70 kDa. Effects of different nitrogrn and carbon sources with different concentrations were also studied. Partially purified enzyme was active at pH of 6.0 for up to 3 h and at temperature of 70 degrees C for 1 h. Ca2+, Mg2+, Ne+1, and K+1 play an important role in increasing enzyme activity. The residual activity of esterase was decreased in the presence of organic solvents. SDS, beta-mercaptoethanol, and DMSO are good inhibitors for esterase enzyme. Under these conditions, partially purified esterase with specific activity of 114.20 U/mg and 47.58 purification fold was obtained. The data achieved from this work are important in terms of heat stability and pH of esterase and giving a new enzyme source for industrial applications.