title: Purification and characterization of a thermostable glucoamylase from Chaetomium thermophilum.
abstract: Thermostable amylolytic enzymes are currently being investigated to improve industrial processes of starch degradation. A thermostable extracellular glucoamylase (exo-1, 4-alpha-D-glucanohydrolase, E.C.3.2.1.3) from the culture supernatant of a thermophilic fungus Chaetomium thermophilum was purified to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) homogeneity by using ammonium sulfate fraction, DEAE-Sepharose Fast Flow chromatography, and Phenyl-Sepharose Fast Flow chromatography. SDS-PAGE of the purified enzyme showed a single protein band of molecular weight 64 kDa. The glucoamylase exhibited optimum catalytic activity at pH 4.0 and 65 degrees C. It was thermostable at 50 degrees C and 60 degrees C, and retained 50% activity after 60 min at 65 degrees C. The half-life of the enzyme at 70 degrees C was 20 min. N-terminal amino acid sequencing (15 residues) was AVDSYIERETPIAWN. Different metal ions showed different effects on the glucoamylase activity. Ca2+, Mg2+, Na+, and K+ enhanced the enzyme activity, whereas Fe2+, Ag+, and Hg2+ cause obvious inhibition. These properties make it applicable to other biotechnological purposes.
authors.affiliation: Department of Environmental Biology, Shandong Agricultural University, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Chen
authors.forename: Duo-Chuan
authors.initials: DC
authors.lastname: Li
authors.forename: Yu-Qin
authors.initials: YQ
authors.lastname: Zhang
authors.forename: Qing-Xin
authors.initials: QX
authors.lastname: Zhou
mesh_terms: D000595:Amino Acid Sequence; D001709:Biotechnology / Q000379:methods; D002597:Chaetomium / Q000201:enzymology* / Q000254:growth & development; D004795:Enzyme Stability; D005087:Glucan 1,4-alpha-Glucosidase / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D013696:Temperature
chemical_list: D005087:Glucan 1,4-alpha-Glucosidase