초록
A β-glucosidase from Gordonia terrae was cloned and expressed in Escherichia coli. The recombinant enzyme with a specific activity of 16.4 U/mg for ginsenoside Rb<SUB>1</SUB> was purified using His-trap chromatography. The purified enzyme specifically hydrolyzed the glucopyranosides at the C-20 position in protopanaxadiol (PPD)-type ginsenosides and hydrolyzed the glucopyranoside at the C-6 or C-20 position in protopanaxatriol (PPT)-type ginsenosides. The reaction conditions for the high-level production of Rg<SUB>3</SUB> from Rb<SUB>1</SUB> by the enzyme were pH 6.5, 30<SUP>o</SUP>C, 20 mg/ml enzyme, and 4 mg/ml Rb<SUB>1</SUB>. Under these conditions, G. terrae β-glucosidase completely converted Rb<SUB>1</SUB> and Re to Rg<SUB>3</SUB> and Rg<SUB>2</SUB>, respectively, after 2.5 and 8 h, respectively. Moreover, the enzyme converted Rg<SUB>1</SUB> to Rh<SUB>1</SUB> at 1 h with a molar conversion yield of 82%. The enzyme at 10 mg/ml produced 1.16 mg/ml Rg<SUB>3</SUB>, 1.47 mg/ml Rg<SUB>2</SUB>, and 1.17 mg/ml Rh<SUB>1</SUB> from Rb<SUB>1</SUB>, Re, and Rg<SUB>1</SUB>, respectively, in 10% (w/v) ginseng root extract at pH 6.5 and 30<SUP>o</SUP>C after 33 h with molar conversion yields of 100%, 100%, and 77%, respectively. The combined molar conversion yield of Rg<SUB>2</SUB>, Rg<SUB>3</SUB>, and Rh<SUB>1</SUB> from total ginsenosides in 10% (w/v) ginseng root extract was 68%. These above results suggest that this enzyme is useful for the production of ginsenosides Rg<SUB>3</SUB>, Rg<SUB>2</SUB>, and Rh<SUB>1.</SUB>