Expression and characterization of thermostable D-allulose 3-epimerase from Arthrobacter psychrolactophilus (Ap DAEase) with potential catalytic activity for bioconversion of D-allulose from d-fructose

A novel D-allulose 3-epimerase (DAEase) from Arthrobacter psychrolactophilus (Ap DAEase) was first characterized in this study. The enzyme catalyzes the epimerization of d-fructose into a functional rare sugar, D-allulose. Ap DAEase was the first record of DAEase identified as a homotrimer with the molecular weight of its subunit at approximately 34 kDa. It had an optimum activity at pH 8.5 and 70 °C in the presence of 1 mM Mg2+. Ap DAEase was found to be an excellent thermostable enzyme. The half-life value at 70 °C was 128.4 min. The kcat and catalytic efficiency of the enzyme toward d-fructose were 2920.00 s-1 and 3.953 mM-1 s-1, respectively. To the best of our knowledge, Ap DAEase possesses the highest kcat among the previously reported DAEases. The conversion ratio of 500 and 100 mg L-1d-fructose to D-allulose was approximately 27 % in 15 and 90 min, respectively. These research findings suggest that Ap DAEase is a promising candidate for the industrial production of D-allulose.