Thermodynamics and kinetic properties of halostable endoglucanase from Aspergillus fumigatus ABK9.

An endoglucanase from Aspergillus fumigatus ABK9 was purified from the culture extract of solid-state fermentation and its some characteristics were evaluated. The molecular weight of the purified enzyme (56.3 kDa) was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, zymogram analysis and confirmed by MALDI-TOF mass spectrometry. The enzyme was active optimally at 50 °C, pH 5.0 and stable over a broad range of pH (4.0-7.0) and NaCl concentration of 0-3.0 M. The pKa1 and pKa2 of the ionizable groups of the active sites were 2.94 and 6.53, respectively. The apparent Km , Vmax , and Kcat values for carboxymethyl cellulose were 6.7 mg ml(-1), 775.4 µmol min(-1) , and 42.84 × 10(4)  s(-1), respectively. Thermostability of the enzyme was evidenced by the high activation energy (91.45 kJ mol(-1)), large enthalpy for activation of denaturation (88.77 kJ mol(-1)), longer half-life (T1/2) (433 min at 50 °C), higher melting temperature (Tm ) (73.5 °C), and Q10 (1.3) values. All the characteristics favors its suitability as halotolerant and thermostable enzyme during bioprocessing of lignocellulosic materials.