초록
A recombinant β-glucosidase from Sphingopyxis alaskensis with a specific activity of 233.3Umg<SUP>-1</SUP> was purified by His-trap chromatography. The native enzyme was a 206kDa tetramer. The maximum enzyme activity was observed at pH 5.5 and 50<SUP>o</SUP>C. However, above 40<SUP>o</SUP>C, the enzyme stability significantly decreased. The enzyme hydrolyzed only the outer glucose at the C-3 position in protopanaxadiol-type ginsenosides without further hydrolysis. Because of the narrow substrate specificity, the enzyme completely converted ginsenosides Rb<SUB>1</SUB>, Rb<SUB>2</SUB>, Rc, and Rd as substrates to gypenoside XVII, compound O, compound Mc<SUB>1</SUB>, and F<SUB>2</SUB>, respectively, and it converted ginsenoside Rg<SUB>3</SUB> to Rh<SUB>2</SUB> with a molar conversion yield of 89%. These results suggest that the recombinant β-glucosidase from S. alaskensis is a potential producer of the rare ginsenosides gypenoside XVII, compound O, compound Mc<SUB>1</SUB>, F<SUB>2</SUB>, and Rh<SUB>2</SUB>. Among ginsenoside substrates, Rb<SUB>1</SUB> was used for the high-level production of the rare ginsenoside gypenoside XVII. The optimum reaction conditions were pH 5.5, 40<SUP>o</SUP>C, 0.5mgml<SUP>-1</SUP> (116.7Uml<SUP>-1</SUP>) enzyme, and 8.0gl<SUP>-1</SUP> ginsenoside Rb<SUB>1</SUB>. Under these conditions, 6.8gl<SUP>-1</SUP> gypenoside XVII was produced by the enzyme after 1h with a molar conversion yield of 100% and a productivity of 6.8gl<SUP>-1</SUP>h<SUP>-1</SUP>.