Recently, rare sugars have caused extensively attention due to their beneficial physiological functions and potential applications in food systems and medical fields. Ketose 3-epimerase (KEase) can catalyze reversibly the epimerization between ketoses which is the pivotal enzyme in Izumoring strategy and an effective tool for biological production of rare sugars. In this work, a KEase from Caballeronia fortuita was recombined and characterized as a d-tagatose 3-epimerase (DTEase, EC 5.1.3.31). The recombinant DTEase displayed the highest activity at pH7.5 and 65°C in the presence of Co2+. The recombinant DTEase displayed the relatively high thermostability and the half-life (t1/2) was determined to be 7.13, 5.13, and 1.05h at 50, 55, and 60°C, respectively. The recombinant DTEase had a wide substrate specificity and the specific activities towards d-tagatose, d-allulose, d-fructose and l-sorbose were measured to be 801±2.3, 450±2.7, 270±1.5 and 55±1.8Umg-1, respectively. So far, the recombinant DTEase exhibited the highest specific activity towards d-tagatose compared with other reported KEases. Furthermore, the recombinant DTEase could produce 314.2g/L d-sorbose from 500g/L d-tagatose and 147.0g/L d-allulose from 500g/L d-fructose, with a transformation ratio of 68.2% and 29.4%, respectively. The recombinant DTEase could realize effectively the transformations between various ketoses and was a prominent candidate for production of rare sugars.
Keywords: Characterization; d-Allulose; d-Sorbose; d-Tagatose 3-epimerase.
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