Characterization of L-rhamnose isomerase from Clostridium stercorarium and its application to the production of D-allose from D-allulose (D-psicose)

To characterize l-rhamnose isomerase (l-RI) from the thermophilic bacterium Clostridium stercorarium and apply it to produce d-allose from d-allulose. A recombinant l-RI from C. stercorarium exhibited the highest specific activity and catalytic efficiency (k cat/K m) for l-rhamnose among the reported l-RIs. The l-RI was applied to the high-level production of d-allose from d-allulose. The isomerization activity for d-allulose was maximal at pH 7, 75 °C, and 1 mM Mn2+ over 10 min reaction time. The half-lives of the l-RI at 65, 70, 75, and 80 °C were 22.8, 9.5, 1.9, and 0.2 h, respectively. To ensure full stability during 2.5 h incubation, the optimal temperature was set at 70 °C. Under the optimized conditions of pH 7, 70 °C, 1 mM Mn2+, 27 U l-RI l−1, and 600 g d-allulose l−1, l-RI from C. stercorarium produced 199 g d-allose l−1 without by-products over 2.5 h, with a conversion yield of 33% and a productivity of 79.6 g l−1 h−1. To the best of our knowledge, this is the highest concentration and productivity of d-allose reported thus far.