• Journal of Microbiology and Biotechnology
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• v.14 no.3
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• pp.584-592
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• 2004

A thermostable $\beta$-glycosidase gene, tfi $\beta$-gly, was cloned from the genomic library of Thermus filiformis Wai33 A1. ifi $\beta$-gly consists of 1,296 bp nucleotide sequence and encodes a polypeptide of 431 amino acids. It shares a strong amino acid sequence similarity with the $\beta$-glycosidases from other Thermus spp. belonging to the glycosyl hydrolase family 1. In the present study, the enzyme was overexpressed in Escherichia coli BL21 (DE3) using the pET21b(+) vector system. The recombinant enzyme was purified to homogeneity by heat treatment and a $Ni^{2+}$-affinity chromatography. Polyacrylamide gel electrophoresis (PAGE) showed that the recombinant Tfi $\beta$-glycosidase was a monomeric form with molecular mass of 49 kDa. The temperature and pH range for optimal activity of the purified enzyme were 80- $90^{\circ}C$ and 5.0-6.0, respectively. Ninety-three percent of the enzyme activity was remained at $70^{\circ}C$ after 12 h, and its half-life at $80^{\circ}C$ was 6 h, indicating that Tfi $\beta$-glycosidase is highly thermostable. Based on its K_m$, or $K_{cat}K_m$, ratio, Tfi $\beta$-glycosidase appeared to have higher affinity for $\beta$-D-glucoside than for $\beta$-D-galactoside, however, $K_{cat} for \beta$-D-galactoside was much higher than that for $\beta$-D-glucoside. The activity for lactose hydrolysis was proportionally increased at $70^{\circ}C$ and pH 7.0 without substrate inhibition until reaching 250 mM lactose concentration. The specific activity of Tfi TEX>$\beta$-glycosidase on 138 mM lactose at $70{^\circ}C$ and pH 7.0 was 134.9 U/mg. Consequently, this newly cloned enzyme appears to have a valuable advantage of conducting biotechnological processes at elevated temperature during milk pasteurization in the production of low-lactose milk.

• Applied Chemistry for Engineering
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• v.31 no.1
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• pp.43-48
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• 2020

Fe₂O₃ nanoparticles with the mixed structure of cubic and nanorod were synthesized by precipitation, hydrothermal, sol-gel method, etching process and heat treatment. Fe₂O₃/TiO₂ core-shell (CS) of type Fe₂O₃@TiO₂ composite was fabricated on a 20 nm nanolayer of TiO₂ coated on the surface of Fe₂O₃ nanoparticles. Fe₂O₃/TiO₂ yolk-shell (YS) composite was prepared by chemical etching and heat treatment of Fe₂O₃/TiO₂ CS nanoparticles. Physical properties of Fe₂O₃, Fe₂O₃@TiO₂ CS and Fe₂O₃@TiO₂ YS nanoparticles were characterized by FE-SEM, HR-TEM and X-ray diffraction. The solar reflectance, commission internationale de l'Elcairage (CIE) color coordinate and heat shield temperatures of Fe₂O₃, CS and YS type Fe₂O₃@TiO₂ pigments filled with poly acrylate (PA) paints were investigated by UV-Vis-NIR spectrometer and homemade heat shield temperature measuring device. The Fe₂O₃@TiO₂ YS red pigment filled PA composite exhibited excellent near infrared light reflecting performance and also reduced the heat shield temperature of 13 ℃ than that of Fe₂O₃ filled counterparts.