Simple and Efficient Production of Highly Soluble Daidzin Glycosides by Amylosucrase from Deinococcus geothermalis

Transglycosylation of amylosucrase from Deinococcus geothermalis (DGAS) was performed using daidzin (daidzein-7-O-glucoside). Unlike cyclodextrin glucanotransferase, DGAS led to the production of new daidzin glucosides with high conversion yields (89%). Structures of these daidzin glucosides (i.e., DA2 and DA3) were daidzein-7-O-alpha-D- glucopyranosyl-(4 -> 1)-O-beta-D-glucopyranoside (daidzin-4 ''-O-alpha-D-glucopyranoside) and daidzein-4'-O-alpha-n-glucopyranosyl-7-O-alpha-D-glucopyranosyl-(1 -> 4)-O-beta-D-glucopyranoside (daidzin-4',4 ''-O-alpha-D-diglucopyranoside), respectively. DA2 and DA3 showed increased solubility of 15.4 mM (127-fold) and 203.3 mM (1686-fold) compared with daidzin, respectively. Kinetic studies revealed V-max of 1.0 mu M/min and K-m' of 175 mu M for DA3 production based on nonlinear regression. DGAS exhibited substrate inhibition behavior at high sucrose concentrations (700-1500 mM). Taken together, these findings indicate that DGAS can attach a glucose unit to a free C-4'-OH via an a-linkage and then produce highly water-soluble isoflavone glycosides with a simple donor, moderate reaction conditions, less waste production, and high yield compared with that observed using the existing processes and enzymes.