Characterization of a d-psicose-producing enzyme, d-psicose 3-epimerase, from Clostridium sp.

The gene coding for d-psicose 3-epimerase (DPEase) from Clostridium sp. BNL1100 was cloned and expressed in Escherichia coli. The recombinant enzyme was purified by Ni-affinity chromatography. It was a metal-dependent enzyme and required Co2+ as optimum cofactor. It displayed catalytic activity maximally at pH 8.0 and 65 °C (as measured over 5 min). The optimum substrate was d-psicose, and the Km, turnover number (kcat), and catalytic efficiency (kcat/Km) for d-psicose were 227 mM, 32,185 min−1, and 141 min−1 mM−1, respectively. At pH 8.0 and 55 °C, 120 g d-psicose l−1 was produced from 500 g d-fructose l−1 after 5 h.