Biochemical characterization of endoglucanases produced by Myceliophthora thermophila M.7.7 in solid-state culture

Abstract

Cellulases have been investigated for their potential application in lignocellulosic residues, used to produce second-generation ethanol (2 GE), as these enzymes can hydrolyze cellulose and release glucose for alcoholic fermentation by yeasts. The aim of this project was to characterize the endoglucanases produced by the thermophilic fungus Myceliophthora thermophila M.7.7 in solid-state cultivation. Tests were carried out with the crude enzyme extract (CEE) to assess the effects of pH, temperature, and various chemicals including cations and phenolic compounds on endoglucanolytic activity. The molecular weight estimation was performed by polyacrylamide gel electrophoresis (SDS-PAGE), and it was possible to observe seven endoglucanases detected by zymography, with estimated Mw in the range between 26 and 82 kDa. The optimum pH for the CEE was 5.5 and the optimum incubation temperature was 70 °C. Concerning endoglucanase stability, the highest activities were achieved in the pH range of 6.0–6.5, and between temperatures of 30 and 40 °C up to 120 min. Among the tested reagents, Triton, dithiotreitol (DTT), and Isopropanol increased the enzymatic activity on the crude extract by about 10%. Among cations, only Sr2+ significantly increased the endoglucanases’ activity. Of the phenolic compounds, although all induced a decrease of the endoglucanolytic activity, none could nullify it after a pre-incubation for 24 h. The apparent kinetic parameters were determined using carboxymethylcellulose (CMC), being Vmax = 51.7 ± 2.7 μmol min−1 and Km = 0.99 ± 0.15 g% CMC (9.9 mg mL−1).