Purification and characterisation of α-amylase produced by mutant strain of Aspergillus oryzae EMS-18

α-Amylase produced by a mutant strain of Aspergillus oryzae EMS-18 has been purified to homogeneity as judged by sodium dodecyle sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme was purified by using 70% ammonium sulphate precipitation followed by anion exchange chromatography on DEAE-Sephadex column and gel filtration on Sephadex G-100. An enzyme purification factor of 9.5-fold was achieved with a final specific activity of 1987.7 U/mg protein and overall yield of 23.8%. The molecular weight of purified α-amylase was estimated to be 48 kDa by SDS-PAGE. The purified enzyme revealed an optimum assay temperature and pH 40°C and 5.0, respectively. Except Ca⁺⁺ all other metal ions such as Mg, Mn, Na, Zn, Ni, Fe, Cu, Co and Ba were found to be inhibitory to enzyme activity.     

Kinetic characterization of extracellular α-amylase from a derepressed mutant ofBacillus licheniformis

Three strains ofBacillus licheniformis were isolated and screened for α-amylase production by solid-state fermentation. Of these, IS-2 gave relatively higher enzyme production (32±2.3 U/[g·min]) and was selected for improvement after treatment withN-methylN-nitroN-nitroso guanidine (NG) or nitrous acid (NA) to enhance its hydrolytic potential. Among the mutant variants, NA-14 gave higher enzyme production (98±1.6 U/[g·min]), and hence, was selected for kinetic and thermal characterization. M1 as a moistening agent (pH 7.0, optimized) supported 2.65-fold improved amylolytic activity by the derepressed mutant 72 h after inoculation. The values of product yield coefficient (Y _p/x=1833.3 U/g) and specific rate constant (q _p=25.46 U/[g·h]) with starch were severalfold improved over those from other carbon sources and the other cultures. The purified enzyme from NA-14 was most active at 40°C; however, the activity remained almost constant up to 44°C. The NA-induced random mutagenesis substantially improved the enthalpy (ΔH _D=94.5±11 kJ/mol) and entropy of activation (ΔS=−284±22 J/[mol·K]) for α-amylase activity and substrate binding for starch hydrolysis. The results of this study (117.8±5.5 U/[g·min]) revealed a concomitant improvement in the endogenous metabolism of the mutant culture for α-amylase production.