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 (KM), maximum velocity V max , thermal inactivation rate constant (ki), half-life (t1/2), and the change of energy due to denaturation (ΔGi). The results showed that the soluble enzyme has an optimum temperature of 55°C, KM of 3.04 mg mL−1 substrate, V max of 10.90 μmole mL−1 min−1, ki of 0.0171 min−1, t1/2 of 40.53 min, and ΔGi of 104.47 kJ mole−1, while the immobilized enzyme has an optimum temperature of 70°C, KM of 8.31 mg mL−1 substrate, V max of 1.44 μmole mL−1 min−1, ki of 0.0060 min−1, t1/2 of 115.50 min, and ΔGi 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.

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 (KM), maximum velocity V max , thermal inactivation rate constant (ki), half-life (t1/2), and transformation of free energy because of denaturation (ΔGi). The free enzyme has optimum temperature of 55°C, KM = 3.04 mg mL−1 substrate, V max = 10.90   μ molemL − 1 min − 1 , ki = 0.0171 min−1, t1/2 = 40.53 min, and ΔGi = 104.47 kJ mole−1. Meanwhile, the immobilized enzyme has optimum temperature of 60°C, KM = 11.57 mg mL−1 substrate, V max = 3.37   μ molemL − 1 min − 1 , ki = 0.0045 min−1, t1/2 = 154.00 min, and ΔGi = 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.

In this paper, the A. fumigatus α-amylase had been immobilized onto zeolite/chitosan hybrid to improve its thermal-stabilization for industrial needs. The methods applied enzyme production, isolation, partial purification, immobilization, and characterization. The optimum temperatures of the native and immobilized enzymes were 50 and 55˚C, respectively. The native enzyme has KM of 3.478 ± 0.271 mg mL-1 substrate and Vmax of 2.211± 0.096 µmole mL-1 min-1, while the immobilized enzyme has KM value of 12.051 ± 4.949 mg mL-1 substrate and Vmax of 1.602 ± 0.576 µmole mL-1 min-1. The residual activity of the immobilized enzyme retained up 10.97% after fifth reuse cycles. The native enzyme has ΔGi of 104.35 ± 1.09 kJ mole-1 and t½ of 38.75 ± 1.53 min, while the immobilized enzyme has ΔGi of 108.03 ± 0.05 kJ mole-1 and t½ of 180.03 ± 3.31 min. According to the increase in half-life (t½), stability improvement of the A. fumigatusα-amylase was 4.65 times greater than the native enzyme. Thus, the zeolite/chitosan hybrid is used as a new supporting matrix for further enzyme immobilization to stabilize the enzymes. Doi: 10.28991/ESJ-2022-06-03-06 Full Text: PDF

In this research, the immobilization of α-amylase from Bacillus subtilis ITBCCB148 by crosslinking method on chitosan matrix has been performed. This research aims to know the effect of immobilization on the thermal stability of α-amylase. The results showed that the native α-amylase has an optimum temperature of  65oC, KM = 1.6 mg mL-1 substrate, and Vmax = 39.7 µmol mL-1 min-1. The immobilized α-amylase has optimum temperature of 75oC, KM = 3.5 mg mL-1 substrate, and Vmax = 7.05 µmol mL-1 min-1. The residual activity of the native and immobilized enzyme on thermal stability test at 65oC for 80 minutes was 58% and 86.15%, respectively. The immobilized enzyme can be reused up to six repeated cycles.The thermodynamic data of native enzyme was t½ = 113.6 min, ki = 6.1x10-3 min-1, and ΔGi = 107.3 kJ mol-1, while the immobilized enzyme was t½ = 433.1 min, ki= 1.6x10-3 min-1, and ΔGi 111.1 kJ mol-1. Based on the decrease of ki, and the increase of ΔGi and half-life(t½) values, the immobilization of α-amylase with chitosan can increase the thermal stability of this enzyme.

The synthesis and comparative study on the antibacterial activity of three organotin(IV) compounds, namely dibutyltin(IV) bis-(3-hydroxybenzoate), [Bu2Sn(3-HBz)2] (7), diphenyltin(IV) bis-(3-hydroxybenzoate), [Ph2Sn(3-HBz)2] (8), and triphenyltin(IV) 3-hydroxybenzoate, [Ph3Sn(3-HBz)] (9) which were prepared by the reaction of dibutyltin(IV) oxide, [Bu2SnO] (4), diphenyltin(IV) dihydroxide, [Ph2Sn(OH)2] (5), and triphenyltin(IV) hydroxide, [Ph3SnOH] (6) with 3-hydroxybenzoic acid (3-HBz) has successfully been performed. The characterization of these compounds were done using 1H and 13C NMR, IR, UV spectroscopies and their compositions were determined based on microanalytical data. Antibacterial activity of these compounds was demonstrated at concentrations of 1.89 × 10−4, 1.81 × 10−4, and 1.72 × 10−4 M, respectively by dilution method against Pseudomonas aeruginosa. Similarly, the compounds were active at concentration of 1.87 × 10−4, 1.79 × 10−4, and 1.71 × 10−4 M, respectively, against Bacillus subtilis. These activities are comparable to that of streptomycin at a concentration of 1.70 × 10−4 M as a positive control, but the halozone of compounds 7, 8, and 9 were slightly lower than that of streptomycin’s halozone. The results obtained suggest that the compounds synthesized have potential as antibacterial agents.