Studies On Purification And Characterization Of β-Glucosidase From The Thermophilic Fungus Cheatomium Thermophilium

The cellulase system in fungi is considered to comprise three hydrolytic enzymes: (i) the endo-(1,4)-beta-D-glucanase (synonyms: endoglucanase, endocellulase, carboxymethyl cellulase [EC 3.2.1.4] ), which cleaves beta-linkages at random, commonly in the amorphous parts of cellulose; (ii) the exo-(l,4)-beta-D-glucanase (synonyms: cellobiohydrolase, exo-cellulase, microcrystalline cellulase, Avicelase [EC 3.2.1.91] ); which releases cellobiose from either the nonreducing or the reducing end, generally from the crystalline parts of cellulose; and (iii) the beta-glucosidase (synonym: cellobiase [EC 3.2.1.21]), which releases glucose from cellobiose and short-chain cellooligosaccharides . Although beta-glucosidase has no direct action on cellulose,. it is regarded as an important component of cellulase system because it stimulates cellulose hydrolysis.Cheatomiu thermophilium, a kind of the thermophilic fungi, is a metatrophic fungus. It can be thrive at the temperature between 45 centigrade and 50 centigrade while most fungi will die above 40 centigrade soonly. And the cellulase system produced by thermophilic fungi will keep higher activities than that of mesophilic fungi at high temperature. Some reports have been published about beta-glucosidase from thermophilic fungi except from Cheatomiu thermophilium.A kind of p-glucosidase from culture supernatant of a thermophilic fungus Cheatomium thermophilium was purified to homogeneity, by using ammonium sulfate fraction, DEAE-sepharose fast-flow chromatography, phenyl-sepharose fast flow chromatography and sephacryl S-100 chromatography, and its properties and substrate specificities were studied in this article. The molecular mass of the enzyme is about between 78.4kDa to 81kDa, as identified by 12.5% SDS-PAGE and gel filtration correspondingly. Its optimum pH value and temperature are 4.5-5.0 and 60 centigrade respectively. It has thermostable activity and the half life time of the enzyme at 70 centigrade is 20min, even will remain 15% activity after 20min at 80 centigrade.Different metal ions show different effects on the P-glucosidase activity. Ca2+ will enhance its activity , while Fe3+, Zn2+will cause some inhibition on it. And the enzyme activity is strongly inhibited by Ag+, Hg2+ and Cu2+. The enzyme acts specially on salicin.