Purification and characterisation of a novel α-L-rhamnosidase exhibiting transglycosylating activity from Aspergillus oryzae

Summary A novel α-L-rhamnosidase was isolated and purified from Aspergillus oryzae NL-1. The enzyme was purified 13.2-fold by ultrafiltration, ion exchange and gel filtration chromatography with an overall recovery of 6.4% and specific activity of 224.4 U/mg, and the molecular mass of its subunit was approximately 75 kDa. Its optimal temperature and pH were 65 °C and 4.5, respectively. The enzyme was stable in the pH range 3.5–7.0, and it showed good thermostability at higher temperatures. The K M , kcat and kcat/K M values were 5.2 m m , 1624 s −1 and 312 s −1 m m −1 using p NPR as substrates, respectively. Moreover, the enzyme exhibited transglycosylating activity, which could synthesise rhamnosyl mannitol through the reactions of transglycosylation with inexpensive rhamnose as the glycosyl donor. Our findings indicate that the enzyme has potential value for glycoside synthesis in the food industry.