Characterization of a thermophilic L-arabinose isomerase from Thermoanaerobacterium saccharolyticum NTOU1

L-Arabinose isomerase (EC 5.3.1.4, L-AI) mainly catalyzes the reversible aldose-ketose isomerization between L-arabinose and L-ribulose. L-AIs can also catalyze other reactions, such as the conversion of D.-galactose to D-tagatose. In this study, the araA gene encoding L-AI was PCR-cloned from Thermoanaerobacterium saccharolyticum NTOU1 and then expressed in Escherichia coli. The recombinant L-AI was purified from the cell-free extract using nickel nitrilotriacetic acid metal-affinity chromatography. The purified enzyme showed an optimal activity at 70 C and pH 7-7.5. The enzyme was stable at pHs ranging from 6.5 to 9.5 and the activity was fully retained after 2 h incubation at 55-65 C. The low concentrations of divalent metal ions, either 0.1 mM Mn2+ or 0.05 mM Co2+, could improve both catalytic activity and thermostability at higher temperatures. The recombinant T. saccharolyticum NTOUI L-AI has the lowest demand for metal ions among all characterized thermophilic L-AIs. This thermophilic L-AI shows a potential to be used in industry to produce D-tagatose from D-galactose. (C) 2013 Elsevier B.V. All rights reserved.