Enzymatic biosynthesis of a puerarin-cycloamylose inclusion complex by 4-α-glucanotransferase and maltogenic amylase

To increase the water solubility of puerarin, an isoflavonoid derived from Radix puerariae, a puerarin inclusion complex with cycloamylose was enzymatically synthesized by combining maltogenic amylase reactions from Bacillus stearothermophilus (BSMA) and 4-alpha-glucanotransferase from Thermus scotoductus (TS alpha GT). The puerarin transfer products, including maltosyl-alpha-(1 -> 6)-puerarin as a major product generated by BSMA, were reacted with TS alpha GT in the presence of amylose. The molecular weights and chemical structures of the reaction products were determined using TLC, HPLC and MALDI-TOF/MS. An analysis of the reaction products revealed that the maltosyl-alpha-(1 -> 6)-puerarin-cycloamylose complex was formed by an elongation reaction and cyclization of TS alpha GT. The results indicate that TS alpha GT does not have substrate affinity towards puerarin or glucosyl alpha-(1 -> 6)-puerarin; however, it did have an affinity towards maltosyl-alpha-(1 -> 6)-puerarin in which the first glucose of the maltosyl residue is linked through an O-glucosidic bond.