ABSTRACT
Enzyme immobilization is a powerful method to improve the stability, reuse, and enzymatic properties of enzymes. The immobilization of the α-amylase enzyme from Aspergillus fumigatus on a chitin-bentonite (CB) hybrid has been studied to improve its stability. Therefore, this study aims to obtain the higher stability of α-amylase enzyme to reduce industrial costs. The procedures were performed as follows: production, isolation, partial purification, immobilization, and characterization of the free and immobilized enzymes. The CB hybrid was synthesized by bentonite, chitin, and glutaraldehyde as a cross-linker. The free enzyme was immobilized onto CB hybrid using 0.1 M phosphate buffer pH 7.5. The free and immobilized enzymes were characterized by optimum temperature, Michaelis constant (K M), maximum velocity (V max), thermal inactivation rate constant (k i ), half-life (t 1/2), and transformation of free energy because of denaturation (ΔG i ). The free enzyme has optimum temperature of 55°C, K M = 3.04 mg mL-1 substrate, V max=10.90 µmolemL-1min-1, k i = 0.0171 min-1, t 1/2 = 40.53 min, and ΔG i = 104.47 kJ mole-1. Meanwhile, the immobilized enzyme has optimum temperature of 60°C, K M = 11.57 mg mL-1 substrate, V max=3.37 µmolemL-1min-1, k i = 0.0045 min-1, t 1/2 = 154.00 min, and ΔG i = 108.17 kJ mole-1. After sixth cycle of reuse, the residual activity of the immobilized enzyme was 38%. The improvement in the stability of α-amylase immobilized on the CB hybrid based on the increase in half-life was four times of the free enzyme.
ABSTRACT
The stability of the α-amylase enzyme has been improved from Aspergillus fumigatus using the immobilization method on a bentonite matrix. Therefore, this study aims to obtain the higher stability of α-amylase enzyme from A. fumigatus; hence, it is used repeatedly to reduce industrial costs. The procedures involved enzyme production, isolation, partial purification, immobilization, and characterization. Furthermore, the soluble enzyme was immobilized using 0.1 M phosphate buffer of pH 7.5 on a bentonite matrix, after which it was characterized with the following parameters such as optimum temperature, Michaelis constant (K M ), maximum velocity (V max), thermal inactivation rate constant (k i), half-life (t 1/2), and the change of energy due to denaturation (ΔG i ). The results showed that the soluble enzyme has an optimum temperature of 55°C, K M of 3.04 mg mL-1 substrate, V max of 10.90 µmole mL-1 min-1, k i of 0.0171 min-1, t1/2 of 40.53 min, and ΔG i of 104.47 kJ mole-1, while the immobilized enzyme has an optimum temperature of 70°C, K M of 8.31 mg mL-1 substrate, V max of 1.44 µmole mL-1 min-1, k i of 0.0060 min-1, t 1/2 of 115.50 min, and ΔG i of 107.37 kJ mole-1. Considering the results, the immobilized enzyme retained 42% of its residual activity after six reuse cycles. Additionally, the stability improvement of the α-amylase enzyme by immobilization on a bentonite matrix, based on the increase in half-life, was three times greater than the soluble enzyme.
ABSTRACT
We report an extremely biocompatible solvent for plant cell walls based on a polar liquid zwitterion that dissolves cellulose, the most recalcitrant component of the plant cell walls. The polar liquid zwitterion does not affect the viability and activity of Escherichia coli, even at high concentrations. We demonstrate conversion of cell walls to ethanol via a starch-like process, namely successive dissolution, hydrolysis and fermentation in the same reaction pot.
