High-efficiency enzymatic production of α-isoquercitrin glucosides by amylosucrase from Deinococcus geothermalis

Isoquercitrin (IQ, quercetin-3-O-β-d-glucopyranoside) has diverse biological functions, such as anti-oxidant and anti-cancer activity, but its use is limited by poor solubility and bioavailability. Enzymatically modified IQ (EMIQ) is a mixture of transglycosylated IQs that have better solubility and bioavailability than do quercetin and IQ. Two different enzymes, cyclodextrin glucanotransferase (CGTase) and amylosucrase (ASase), have the transglycosylation activity to produce EMIQ. Both enzymes produce a variety of EMIQs including IQ, IQ-glucoside (IQ-G1), IQ-diglucoside (IQ-G2), and IQ-triglucoside (IQ-G3). ASase had a higher bioconversion yield from IQ to EMIQ (97.6%) than did CGTase (76.8%). In addition, the yield of IQ-G3, which was the most bioavailable form, was higher with ASase (46%) than with CGTases (8%). Taken together, these results suggest that ASase can be used to synthesize EMIQ in a simple and specific process.