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-α-d-glucopyranosyl-(4 → 1)-O-β-d-glucopyranoside (daidzin-4″-O-α-d-glucopyranoside) and daidzein-4′-O-α-d-glucopyranosyl-7-O-α-d-glucopyranosyl-(1 → 4)-O-β-d-glucopyranoside (daidzin-4′,4″-O-α-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 Vmax of 1.0 μM/min and K′m of 175 μM 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 C4′–OH via an α-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.