Purification and characterization of an extracellular β-glucosidase produced by phoma sp. KCTC11825BP isolated from rotten mandarin peel

A β-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 β-glucosidase evidenced high homology with the fungal β-glucosidases belonging to glycosyl hydrolase family 3. Its optimal activity was detected at pH 4.5 and 60^oC, and the enzyme had a half-life of 53 h at 60^oC. The K_m values for p-nitrophenyl-β-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-δ-lactone (K_i=0.1 mM) when pNPG was used as the substrate. Its activity was inhibited by 41% by 10 mM Cu²⁺ and stimulated by 20% by 10 mM Mg²⁺.