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Towards efficient enzymatic conversion of D-galactose to D-tagatose: purification and characterization of L-arabinose isomerase from Lactobacillus brevis

Du, Mengge, Zhao, Dongying, Cheng, Sisi, Sun, Di, Chen, Ming, Gao, Ziqing, Zhang, Chunzhi
Bioprocess and biosystems engineering 2019 v.42 no.1 pp. 107-116
Lactobacillus brevis, arabinose, barium, biotransformation, calcium, catalysts, cobalt, copper, enzyme activity, galactose, gels, ions, isomerases, isomerization, magnesium, manganese, molecular weight, pH, polyacrylamide gel electrophoresis, tagatose, temperature
L-arabinose isomerase (L-AI) (EC 5. 3. 1. 4. L-AI) that mediates the isomerization of D-galactose to D-tagatose was isolated from Lactobacillus brevis (MF 465792), and was further purified and characterized. Pure enzyme with molecular weight of 60.1 kDa was successfully obtained after the purification using Native-PAGE gel extraction method, which was a monomer in solution. The L-AI was found to be stable at 45–75 °C, and at pH 7.0–9.0. Its optimum temperature and pH was determined as 65 °C and 7.0, respectively. Besides, we found that Ca²⁺, Cu²⁺, and Ba²⁺ ions inhibited the enzyme activity, whereas the enzyme activity was significantly enhanced in the presence of Mg²⁺, Mn²⁺, or Co²⁺ ions. The optimum concentration of Mn²⁺ and Co²⁺ was determined to be 1 mM. Furthermore, we characterized the kinetic parameters for L-AI and determined the Kₘ (129 mM) and the Vₘₐₓ (0.045 mM min⁻ ¹) values. Notably, L. brevisL-AI exhibited a high bioconversion yield of 43% from D-galactose to D-tagatose under the optimal condition, and appeared to be a more efficient catalyst compared with other L-AIs from various organisms.