Biochemical characterization of a d ‐psicose 3‐epimerase from Treponema primitia ZAS ‐1 and its application on enzymatic production of d ‐psicose

BACKGROUND The rare sugar d ‐psicose is a hexoketose monosaccharide and a C‐3 epimer of d ‐fructose. d ‐Psicose is a novel functional sweetener with 70% of the sweetness but only 0.3% of the energy content of sucrose. Generally, the industrial production of d ‐psicose involves a bioconversion from d ‐fructose induced by ketose 3‐epimerases. RESULTS The d ‐psicose 3‐epimerase ( DPEase ) gene from Treponema primitia ZAS ‐1 ( Trpr ‐ DPEase ) was cloned and overexpressed in Escherichia coli BL21 ( DE3 ). The recombinant enzyme was purified with a molecular mass of 33 kDa . Trpr ‐ DPEase exhibited optimal activity at pH 8.0 and 70 °C and was sensitive to temperature, with relative thermal stability below 50 °C. It was strictly metal‐dependent and displayed maximum catalytic activity with 450 µmol L −1 Co 2+ . The K m values of the enzyme for d ‐psicose and d ‐fructose were 209 and 279 mmol L −1 respectively. The d ‐psicose/ d ‐fructose equilibrium ratio of Trpr ‐ DPEase was 28:72. CONCLUSION A novel DPEase from T. primitia ZAS ‐1 was characterized that could catalyze the formation of d ‐psicose from d ‐fructose. d ‐Psicose was produced at a yield of 137.5 g L −1 from 500 g L −1 d ‐fructose, suggesting that Trpr ‐ DPEase might be appropriate for the industrial production of d ‐psicose. © 2015 Society of Chemical Industry