Applied Biochemistry and Biotechnology

, Volume 141, Issue 2–3, pp 251–264 | Cite as

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

  • Ikram-ul-Haq
  • Hamad Ashraf
  • Sikander Ali
  • M. A. Qadeer


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.

Index Entries

Bacillus licheniformis α-amylase mutant solid-state fermentation wheat bran thermal characterization 


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Copyright information

© Humana Press Inc 2007

Authors and Affiliations

  • Ikram-ul-Haq
    • 1
  • Hamad Ashraf
    • 1
  • Sikander Ali
    • 1
  • M. A. Qadeer
    • 1
  1. 1.Institute of Industrial BiotechnologyGC University LahorePakistan

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