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

Abstract

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 1mM Mn2+ over 10min reaction time. The half-lives of the L-RI at 65, 70, 75, and 80°C were 22.8, 9.5, 1.9, and 0.2h, respectively. To ensure full stability during 2.5h incubation, the optimal temperature was set at 70°C. Under the optimized conditions of pH 7, 70°C, 1mM Mn2+, 27 U L-RI l-1, and 600g D-allulose l-1, L-RI from C. stercorarium produced 199g D-allose l-1 without by-products over 2.5h, with a conversion yield of 33% and a productivity of 79.6g l-1 h-1. To the best of our knowledge, this is the highest concentration and productivity of D-allose reported thus far.