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Abstract

L-Ribose isomerase (L-RI) catalyzes the aldose-ketose isomerization between L-ribose and L-ribulose. In this study, a putative L-RI gene of Geodermatophilus obscurus DSM 43160 was cloned by PCR into pET-15b and pET-21b, respectively. The cloned target gene was expressed in Escherichia coli. The recombinant N-His-tagged and C-His-tagged proteins exhibited L-RI activity. Both N- and C-His-tagged L-RIs were purified from cell-free extracts by metal-affinity and ionexchange chromatography. The purified N-His-tagged L-RI demonstrated its optimal activity at 30-40°C and pH of 9 (in glycine-NaOH buffer). The enzyme was stable at pH 7-9 and more than 90% activity was retained after incubation at 40°C for 2 h. Metal ions were not required for N-His-tagged L-RI activity to occur, but Hg2+ inhibited its activity completely. The conversion rates of L-arabinose to L-ribose by combining Thermoanaerobacterium saccharolyticum NTOU1 L-arabinose isomerase and G. obscurus DSM43160 N-His-tagged L-RI at 30°C and 40°C were 15.9% and 12.5% (mol mol-1), respectively. Results obtained from this study suggest a potential application of this recombinant L-RI for the L-ribose production from L-arabinose.

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