Properties of D-allulose 3-epimerase mined from Novibacillus thermophilus and its application to synthesis of D-allulose

Allulose is an epimer of D-fructose with multiple nutritional functions, which can be biologically synthesized from D-fructose employing D-allulose 3-epimerase (DAE). In this study, NCBI database mining approach was applied to screen novel DAEs, and Novibacillus thermophilus DAE (NtDAE) exhibiting a high activity of 273.9 U/(g.wet cell weight) was selected for investigation. NtDAE showed optimum reaction temperature and pH at 70 degrees C and 7.0, respectively. In the presence of Co2+, its activity was improved by 100.1 %, and the half-life (t(1/2)) values reached up to 846.3, 539.2 and 47.8 min at 40, 50 and 60 degrees C, respectively. Higher k(cat)/K-m values toward D-allulose indicated that the preferred physiological substrate of NtDAE was D-allulose. The conversion yield of 500 g/L D-fructose to D-allulose at 60.C achieved 29.7 %, and further enhanced to 51.6 % with adding 1.1 M borate. This study provided a useful guidance of further engineering and application of NtDAE for realization of industrial production of D-allulose.