Purification and Characterization of an α‐L‐Rhamnosidase from Aspergillus terreus of Interest in Winemaking

An enzyme with α‐L‐rhamnosidase activity was purified to homogeneity from a culture filtrate of Aspergillus terreus after growth in a medium containing L‐rhamnose as the sole carbon source. The biosynthesis of this enzyme was repressed by glucose. The enzyme had a molecular mass of 96 kDa on sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and an isoelectric point of 4.6 as determined by analytical isoelectric focusing. The pH and temperature optima for the enzyme were found to be 4.0 and 44 °C, respectively. Using p‐nitrophenyl‐α‐L‐rhamnopyranoside as a substrate, the enzyme exhibited Michaelis‐Menten kinetics with K M and V max values of 0.17 mM and 84 U/mg, respectively. The enzyme was inhibited competitively by L‐rhamnose (K 1 2.5 mM). Divalent cations such as Ca 2+ Mg 2+ Zn 2+ and Co 2+ stimulated the a‐L‐rhamnosidase activity, whereas this was inhibited by Hg2+ and Cd2+. Ethanol (12% v/v) and glucose (21% w/v) decreased enzyme activity by approximately 20%, while this was not affected by SO 2 .