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

Abstract

Heptose is a rare monosaccharide with seven carbon atoms. In this study, we demonstrated that two 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 four heptoses could be produced, and that the optimal reaction temperature and donor and acceptor substrate concentration are 50°C and 500 mM, 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-TEcould catalyze epimerization reaction between D-sedoheptulose and D-alloheptulose.