Efficient production of d-sedoheptulose using transketolase from Thermus thermophilus HB8 and epimerization reaction using d-tagatose 3-epimerase from Pseudomonas cichorii ST24.

Heptose is a rare monosaccharide with 7 carbon atoms. In this study, we demonstrated that 2 heptoses can be produced cost-effectively and efficiently using transketolase from Thermus thermophilus HB8 (TtTK). First, alternative substrates to a conventional donor substrate, lithium hydroxypyruvate, were investigated, suggesting that 5-keto-d-fructose (5-KF) was the best donor substrate among the 14 donor substrates evaluated. Using 5-KF and aldopentoses as acceptors, we confirmed that 4 heptoses could be produced, and that the optimal reaction temperature and donor and acceptor substrate concentration are 50 °C and 500 m m, respectively. Furthermore, the d-sedoheptulose produced by the partially purified TtTK was converted to d-allopeptulose through the epimerization by d-tagatose 3-epimerase (d-TE) from Pseudomonas cichorii ST24. The equilibrium ratio of the epimerization reaction between d-sedoheptulose and D-alloheptulose was 45:55. This is the first report that d-TE could catalyze an epimerization reaction between d-sedoheptulose and d-alloheptulose.