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

Abstract

A monomeric feruloyl esterase (FAE) with a molecular mass of 62kDa 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 pH5.0 and at 50°C. The enzyme displayed relatively high thermostability as evidenced by over 70% residual activity at 70°C and about 34% residual activity at 80°C. The K m and V max for this enzyme on methyl ferulate were 0.19mM and 1.65U/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 Mn(2+), Ca(2+), Cd(2+), Zn(2+), Mg(2+), Cu(2+), and K(+) ions but inhibited by Al(3+), Hg(2+), Fe(2+), and Pb(2+) ions at a tested concentration of 2. 5mM.