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 °C and 7.0, respectively. In the presence of Co2+, its activity was improved by 100.1 %, and the half-life (t1/2) values reached up to 846.3, 539.2 and 47.8 min at 40, 50 and 60 °C, respectively. Higher kcat/Km 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.