Purification and characterization of β-galactosidase from Aspergillus fumigatus PCSIR-2013

Extra cellular beta-galactosidase enzyme was purified and characterized from Aspergillus fumigatus PCSIR-2013. Estimated molecular mass of the enzyme was approximately 95 kDa. by native polyacrylamide gel electrophoresis. Initially, different fermentation parameters were optimized for maximum production of beta-galactosidase. The kinetic study of the partially purified enzyme exhibited that it remained active in broad range of temperature from 25 degrees C to 70 degrees C with an optimum of 60 degrees C. The Km and Vmax were calculated as 9.95mmol/l and 51.78 U/ml/min, respectively. The optimum pH was 5.0, when reaction mixture was incubated for 30 min. The enzyme was very stable in the presence of different metal ions, although Na+ (16%) stimulates the activity at 10mM concentration. In contrast, Ba+2 and Hg+2 have negative effect on enzyme activity and activity decreased to 54% and 19%, respectively. Thermo stability study was revealed that the enzyme retained 72% of its activity at 50 degrees C. Whereas, when enzyme was incubated at 60 degrees C for 120 min, its residual activity was decreased to 42.0%. However, the enzyme was completely inactivated at 80 degrees C after 120 min of pre-incubation. Among different surfactant which incorporated with enzyme, Tween 20 and Triton X-100 both have stimulatory effect and activity increased to 29% and 17%, respectively.