Production of d-aldotetrose from l-erythrulose using various isomerases.

d-Aldotetroses are rare sugars are obtained via chemical synthesis in low yield. In this study, we demonstrated that D-aldotetroses could be produced using three isomerases. First, L-erythrulose was epimerized using D-tagatose 3-epimerase from Pseudomonas cichorii ST-24. The specific optical rotation of the reaction solution gradually decreased to zero, indicating that approximately 50% of the L-erythrulose was converted to D-erythrulose. D, L-Erythrulose mixture was isomerized with D-arabinose isomerase from Klebsiella pneumoniae 40bXX to produce D-threose, resulting in a conversion rate of 9.35%. D-erythrose production using L-rhamnose isomerase from Pseudomonas stutzeri LL172 resulted in a conversion rate of 12.9%. Because of the low purity of the purchased D-erythrose, the product was reduced by the Raney nickel catalyst, compared with authentic erythritol. We confirmed the products using HPLC and 13C-NMR spectra. This is the first report of D-aldotetrose production using an enzymatic reaction.