Isolation and Properties of an Extracellular β-Glucosidase from a Filamentous Fungus, Cladosporium resinae, Isolated from Kerosene.

An extracellular β-glucosidase was purified from a culture filtrate of the fungus Cladosporium resinae strain NK-1 grown on a medium containing starch, Tween 80, and yeast extract. The purified enzyme was monomeric with an Mr 98,000, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and native gel filtration using HPLC. The enzyme had optimal activity with p-nitrophenyl-β-D-glucoside (PNPG) at 50°C and pH 4.5. The enzyme catalyzed the hydrolysis of cellobiose and PNPG. The Km and Vmax with PNPG as the substrate at 50°C and pH 4.5 were 0.07 mM and 364 μmol/min/mg, respectively; with cellobiose as the substrate, the corresponding values were 2.3 mM and 75 μmol/min/mg. The enzyme activity was competitively inhibited by glucose (Ki=20 mM), while fructose, galactose, mannose, arabinose, xylose (each at 50 mM), sucrose, and lactose (each at 30 mM) were not inhibitory. While the enzyme has activity against sophorose (β-1,2-glucobiose) and laminaribiose (β-1,3-glucobiose), it has no activity against gentiobiose (β-1,6-glucobiose). The activity of the β-glucosidase was inhibited by Ag(+), Fe(2+), Mn(2+), Zn(2+), Hg(2+), SDS, and p-chloromercuribenzoate.