A Feruloyl Esterase (FAE) Characterized by Relatively High Thermostability from the Edible Mushroom Russula virescens

A monomeric feruloyl esterase (FAE) with a molecular mass of 62 kDa was acquired from fresh fruiting bodies of the edible mushroom Russula virescens. The isolation procedure involved ion exchange chromatography on CM-cellulose, Q-Sepharose, and SP-Sepharose and finally fast protein liquid chromatography-gel filtration on Superdex 75. Two amino acid sequences were obtained after tryptic digestion, and they both showed some homology with the esterase of some fungi. Maximal activity was observed at pH 5.0 and at 50 degrees C. The enzyme displayed relatively high thermostability as evidenced by over 70% residual activity at 70 degrees C and about 34 % residual activity at 80 degrees C. The K-m and V-max for this enzyme on methyl ferulate were 0.19 mM and 1.65 U/mg proteins, respectively. The purified FAE prefers methyl ferulate over methyl caffeate and is least active on methyl p-coumarate. The FAE activity was not significantly affected by the presence of cations such as Mn2+, Ca2+, Cd2+, Zn2+, Mg2+, Cu2+, and K+ ions but inhibited by Al3+, Hg2+, Fe2+, and Pb2+ ions at a tested concentration of 2. 5 mM.