Biochemical identification of a hyperthermostable l-ribulose 3-epimerase from Labedella endophytica and its application for d-allulose bioconversion.

Abstract Currently, low sugar and low energy have become an important trend in the food industries. Therefore, the bioconversion of the functional low-calorie rare sugars attracts more and more attention. l -Ribulose 3-epimerase (LREase) belongs to the ketose 3-epimerase (KEase) family, which could not only efficiently catalyze the reversible C-3 epimerization between l -ribulose and l -xylulose but also between d -fructose and d -allulose. In this paper, a hyperthermostable LREase from Labedella endophytica was identified and characterized. It exhibited maximum catalytic activity at pH 6.0 and 80 °C with 1 mM Ni2+. In the presence of Co2+, the t1/2 values at 60, 65, and 70 °C were 37.7, 9.0, and 4.6 h, respectively, and Tm value was 80.9 °C. From 500 g/L d -fructose, it could produce 154.2 g/L d -allulose with a conversion rate of 30.8% in 10 h. In view of its strong thermostability and high catalytic efficiency, L. endophytica LREase might be a good potential alternative for d -allulose industrial production.