title: Purification and characterization of two thermostable acetyl xylan esterases from Thermoanaerobacterium sp. strain JW/SL-YS485.
abstract: Two acetyl esterases (EC 3.1.1.6) were purified to gel electrophoretic homogeneity from Thermoanaerobacterium sp. strain JW/SL-YS485, an anaerobic, thermophilic endospore former which is able to utilize various substituted xylans for growth. Both enzymes released acetic acid from chemically acetylated larch xylan. Acetyl xylan esterases I and II had molecular masses of 195 and 106 kDa, respectively, with subunits of 32 kDa (esterase I) and 26 kDa (esterase II). The isoelectric points were 4.2 and 4.3, respectively. As determined by a 2-min assay with 4-methylumbelliferyl acetate as the substrate, the optimal activity of acetyl xylan esterases I and II occurred at pH 7.0 and 80 degrees C and at pH 7.5 and 84 degrees C, respectively. Km values of 0.45 and 0.52 mM 4-methylumbelliferyl acetate were observed for acetyl xylan esterases I and II, respectively. At pH 7.0, the temperatures for the 1-h half-lives for acetyl xylan esterases I and II were 75 degrees and slightly above 100 degrees C, respectively.
authors.affiliation: Department of Microbiology, University of Georgia, Athens 30602, USA.
authors.forename: W
authors.initials: W
authors.lastname: Shao
authors.forename: J
authors.initials: J
authors.lastname: Wiegel
mesh_terms: D000115:Acetylesterase / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D000595:Amino Acid Sequence; D001421:Bacteria, Anaerobic / Q000201:enzymology* / Q000235:genetics; D004795:Enzyme Stability; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011487:Protein Conformation; D013379:Substrate Specificity; D014468:Umbelliferones
chemical_list: D014468:Umbelliferones; D000115:Acetylesterase; C081851:acetylxylan esterase