title: Purification and characterization of an extremely thermostable beta-glucosidase from the hyperthermophilic archaeon Pyrococcus furiosus.
abstract: Cell-free extracts of cellobiose-grown cells of the hyperthermophile Pyrococcus furiosus contain very high activities (19.8 U/mg) of a beta-glucosidase. The cytoplasmic enzyme was purified 22-fold to apparent homogeneity, indicating that the enzyme comprises nearly 5% of the total cell protein. The native beta-glucosidase has a molecular mass of 230 +/- 20 kDa, composed of 58 +/- 2-kDa subunits. The enzyme has a pI of 4.40. Thiol groups are not essential for activity, nor is the enzyme dependent on divalent cations or a high ionic strength. The enzyme shows optimum activity at pH 5.0 and 102-105 degrees C. From Lineweaver-Burk plots, Vmax values of 470 U/mg and 700 U/mg were found for cellobiose (Km = 20 mM) and p-nitrophenyl-beta-D-glucopyranoside (Km = 0.15 mM), respectively. The purified enzyme also exhibits high beta-galactosidase activity and beta-xylosidase activity, but shows no activity towards alpha-linked disaccharides or beta-linked polymers, like cellulose. The purified beta-glucosidase shows a remarkable thermostability with a half life of 85 h at 100 degrees C and 13 h at 110 degrees C.
authors: Department of Microbiology, Wageningen Agricultural University, The Netherlands.
authors: S W
authors: SW
authors: Kengen
authors: E J
authors: EJ
authors: Luesink
authors: A J
authors: AJ
authors: Stams
authors: A J
authors: AJ
authors: Zehnder
mesh_terms: D001105:Archaea / Q000201:enzymology* / Q000254:growth & development; D002240:Carbohydrate Sequence; D002384:Catalysis; D002474:Cell-Free System; D002475:Cellobiose / Q000378:metabolism; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D004795:Enzyme Stability; D006358:Hot Temperature; D007700:Kinetics; D008969:Molecular Sequence Data; D013379:Substrate Specificity; D001617:beta-Glucosidase / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D002475:Cellobiose; D001617:beta-Glucosidase