PURIFICATION AND CHARACTERIZATION OF AN ALPHA-L-RHAMNOSIDASE FROM ASPERGILLUS-NIGER

An enzyme with alpha-L-rhamnosidase activity was purified by anion exc hange chromatography from an Aspergillus niger commercial preparation. The alpha-L-rhamnosidase was shown to be N-glycosylated, and had a mo lecular mass of 85 kD on sodium dodecylsulfate-polyacrylamide gel elec trophoresis of which approximately 12% was contributed by carbohydrate . The enzyme was optimally active al pH 4.5 and 65 degrees C. When tes ted towards p-nitrophenyl-alpha-L-rhamnopyranoside it showed K-m and V -max values of 2.9 mM and 20.6 U mg(-1), respectively whereas it was i nhibited competitively by L-rhamnose (K-i 3.5 mM). Substrate specifici ty studies showed alpha-L-rhamnosidase to be active both on alpha-1,2 and alpha-1,6 linkages to beta-D-glucose. Moreover, the enzyme was abl e to release L-rhamnose from geranyl-beta-D-rutinoside and 2-phenyleth yl-beta-D-rutinoside.