Fig. 4

The reactions of steviol monoglucosides by UGT76G1. Direct MS of the single sugar transfer at R1 (a) and R2 position (b) of two self-made steviol monoglucosides. The reaction of the steviol monoglucoside was catalyzed by 0.03 mg ml⁻¹ UGT76G1 (1×) for 18 h. The reaction schemes to synthesize steviol monoglucosides and the single sugar transfer catalyzed by UGT76G1 are shown. The main negative ions derived from the products are labeled and related to the chemical compounds in the reaction schemes. The reaction conditions for these two self-made steviol glucosides are identical, and the relative contents of the substrate (M) and the product (P) show the preferred reaction at the R1 position