Purification and characterization of an extracellular β‐glucosidase from Sporothrix schenckii

摘要

An extracellular β‐glucosidase ( E.C. 3.2.1.21 ), induced by cellulose in the mycelial form of human pathogen fungus Sporothrix schenckii, was purified to homogeneity using hydroxyapatite (HAp) adsorption chromatography in batch and Sephacryl S200‐HR size exclusion chromatography. The molecular mass of the purified enzyme was estimated to be 197 kDa by size exclusion chromatography with a subunit of 96.8 kDa determined by SDS/PAGE. The β‐glucosidase exhibited optimum catalytic activity at pH 5.5/45 °C and was relatively stable for up to 24 h at 45 °C. Isoelectric focusing displayed an enzyme with a pI value of 4.0. Its activity was inhibited by Fe2+ but not by any other ions or chelating agents. K _m and V _max values of the purified enzyme were 0.012 m m and 2.56 nmol·min?1·mg?1, respectively, using 4‐methylumbelliferyl β‐D‐glucopyranoside (4‐MUG) as the substrate and 44.14 m m and 22.49 nmol·min?1·mg?1 when p ‐nitrophenyl β‐D‐glucopyranoside ( p ‐NPG) was used. The purified β‐glucosidase was active against cellobioside, laminarin, 4‐MUG, and p ‐NPG and slightly active against 4‐methylumbelliferyl β‐D‐cellobioside and p ‐nitrophenyl β‐D‐cellobioside but did not hydrolyze 4‐methylumbelliferyl β‐D‐xyloside, 4‐methylumbelliferyl β‐D‐galactopyranoside nor 4‐methylumbelliferyl α‐D‐glucopyranoside. In addition, the enzyme showed transglycosylation activity when it was incubated along with different oligosaccharides. Whether the transglycosylation and cellulase activities function in vivo as a mechanism involved in the degradation of cellulolytic biomass in the saprophytic stage of S. schenckii remains to be determined.