Characterization of an epilactose-producing cellobiose 2-epimerase from Thermoanaerobacterium saccharolyticum

• 2-CE is characterized from a thermoacidophilic bacterium, T. saccharolyticum.
• The enzyme shows maximum activity at 60 °C and pH 7.0.
• It produces epilactose as the only product from lactose.
• Conversion ratio of lactose to epilactose is 25%.

In this study, a recombinant cellobiose 2-epimerase (GenBank accession number, YP_006392930.1) was characterized from a thermophilic bacterium, Thermoanaerobacterium saccharolyticum JW/SL-YS485. The enzyme was metal independent, showed maximal epimerization activity at pH 7.0 and 60 °C, and displayed 29.8, 15.48, and 13.5 U mg−1 for mannobiose, cellobiose, and lactose under optimum conditions, respectively. It exhibited promising thermostability under incubation below 60 °C. The Km, turnover number (kcat), and catalytic efficiency (kcat/Km) for lactose were 124.7 mM, 30.9 s−1, and 0.248 mM−1 s−1, respectively. At pH 7.0 and 60 °C, 50 mM epilactose was produced from 200 mM lactose by a 0.6 μM of enzyme concentration after reaction for 4 h.

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