Thermal Inactivation Kinetics and Secondary Structure Change of a Low Molecular Weight Halostable Exoglucanase from a Marine Aspergillus niger at High Salinities

Abstract

Two kinds of exoglucanase were purified from a marine Aspergillus niger. Catalytic ability of halophilic exoglucanase with a lower molecular weight and secondary structure change was analyzed at different salinities. Activity of the low molecular weight exoglucanase in 10% NaCl solution (w/v) was 1.69-fold higher of that in NaCl-free solution. Half-life time in 10% NaCl solution (w/v) was over 1.27-fold longer of that in NaCl-free solution. Free energy change of the low molecular weight exoglucanase denaturation, △G, in 10% NaCl solution (w/v) was 0.54kJ/mol more than that in NaCl-free solution. Melt point in 10% NaCl solution (w/v), 52.01°C, was 4.21°C higher than that in NaCl-free solution, 47.80°C. K m value, 0.179mg/ml in 10% NaCl solution (w/v) was less 0.044mg/ml than that, 0.224mg/ml, in NaCl-free solution. High salinity made content of α-helix increased. Secondary structure change caused by high salinities improved exoglucanase thermostability and catalysis activity. The halophilic exoglucanase from a marine A. niger was valuable for hydrolyzing cellulose at high salinities.