Abstract: Dioscorea nipponica is a popular herb in China. It has been wildly used to prevent bronchial and other respiratory infections as well as viral infections to treat rheumatic diseases, to improve cardiovascular conditions, to treat and reduce the risk of heart disease and to protect against cancer. The enzymatic transforming generally improves the bioactivity of natural productions. In this paper, dioscin-α-L-rhamnosidase hydrolyzing α-L-rhamnoside from dioscin was found and purified from sheep liver by means of centrifugation, ammonium sulfate precipitation and ion-exchange chromatography on DEAE-cellulose column, and its partial cha-racteristics were studied. A 19.9-fold purification factor was achieved by DEAE-cellulose column. The enzyme showed the highest activity under the reaction condition of pH=6.8, 42 ℃, 8 h, and 23 mmol/L of substrate concentration. In the concentration range of 10—250 mmol/L, ions Fe³⁺, Cu²⁺ strongly inhibited the enzyme, Mg²⁺ and Zn²⁺ slightly activated the enzyme, but Ca²⁺ activated strongly the enzyme. The molecular weight of the enzyme estimated by SDS-PAGE was about 71000. In the comparative examination with rutin-α-L-rhanmosidase, ginsenoside-α-L-rhamnosidase, and α-L-rhamnosidase on the substrates such as dioscin, ginsenoside Re, rutin, it was found that the enzyme has a narrow substrate specificity.

Key words: Dioscin-α-L-rhamnosidase, Sheep liver, Enzyme molecular weight, Hydrolysis activity