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 K _m, turnover number (k _cat), and catalytic efficiency (k _cat/K _m) 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.