Purification and characterization of an intracellular α-l-rhamnosidase from a newly isolated strain, Alternaria alternata SK37.001

Abstract A strain, Alternaria alternata SK37.001, which produces an intracellular α- l -rhamnosidase, was newly isolated from citrus orchard soil. The molecular mass of the enzyme was 66 kDa, as evaluated by SDS-PAGE and 135 kDa, as determined by gel filtration, which indicated that the enzyme is a dimer. The enzyme had a specific activity of 21.7 U mg −1 after step-by-step purification. The optimal pH and temperature were 5.5 and 60 °C, respectively. The enzyme was relatively stable at a pH of 4.0–8.0 and a temperature between 30 and 50 °C compared with other pH levels and temperatures investigated. The enzyme activity was accelerated by Ba 2+ and Al 3+ but inhibited by Ni 2+ , Cu 2+ and Co 2+ , especially Ni 2+ . The kinetic parameters of K m and V max were 4.84 mM and 53.1 μmol mg −1  min −1 , respectively. The α- l -rhamnosidase could hydrolyze quercitrin, naringin and neohesperidin, hesperidin and rutin rhamnose-containing glycosides but could not hydrolyze ginsenoside Rg2 or saiko-saponin C.