Purification and Characterization of an Extracellular ${\beta}$-Glucosidase Produced by Phoma sp. KCTC11825BP Isolated from Rotten Mandarin Peel

A ${\beta}$-glucosidase from Phoma sp. KCTC11825BP isolated from rotten mandarin peel was purified 8.5-fold with a specific activity of 84.5 U/mg protein. The purified enzyme had a molecular mass of 440 kDa with a subunit of 110 kDa. The partial amino acid sequence of the purified ${\beta}$-glucosidase evidenced high homology with the fungal ${\beta}$- glucosidases belonging to glycosyl hydrolase family 3. Its optimal activity was detected at pH 4.5 and $60^{\circ}C$, and the enzyme had a half-life of 53 h at $60^{\circ}C$. The $K_m$ values for p-nitrophenyl-${\beta}$-D-glucopyranoside and cellobiose were 0.3 mM and 3.2 mM, respectively. The enzyme was competitively inhibited by both glucose ($K_i$=1.7 mM) and glucono-${\delta}$-lactone ($K_i$=0.1 mM) when pNPG was used as the substrate. Its activity was inhibited by 41% by 10 mM $Cu^{2+}$ and stimulated by 20% by 10 mM $Mg^{2+}$.