title: Purification and properties of a beta-1,4-xylanase from a cellulolytic extreme thermophile expressed in Escherichia coli.
abstract: 1. An endoxylanase (EC 3.2.1.8) was purified from an Escherichia coli strain carrying a xylanase gene from the extreme thermophile "Caldocellum saccharolyticum" strain Tp8T6.3.3.1. It was found to have an M(r) of 42,000 and an isoelectric point of approx. 5.0. 2. The enzyme showed optimum activity at pH 5.0-7.7 and had an activation energy of 44 kJ mol-1. It was stable at room temperature at pH 4.5-11.5 in the presence of 0.5 mg ml-1 bovine serum albumin. The half-life of the enzyme at 75 degrees C was 20 min at pH 6.0 in the presence of 0.5 mg ml-1 bovine serum albumin. 3. The xylanase had highest activity on oat spelts xylan, releasing xylobiose and some xylotriose. The Km for oat spelts xylan was 0.021% (w/v) at pH 6.0. 4. The enzyme had high activity on sugar cane bagasse hemicelluloses A and B, lower activity on larchwood xylan and also hydrolysed carboxymethylcellulose, 4-methylumbelliferyl beta-D-cellobioside and p-nitrophenyl beta-D-cellobioside, but could not hydrolyse xylobiose. 5. It showed transferase activity on p-nitrophenyl beta-D-xylopyranoside. Xylose did not inhibit the enzyme.
authors: Microbial Biochemistry and Biotechnology Research Unit, University of Waikato, Hamilton, New Zealand.
authors: L R
authors: LR
authors: Schofield
authors: R M
authors: RM
authors: Daniel
mesh_terms: D001419:Bacteria / Q000201:enzymology*; D043364:Endo-1,4-beta Xylanases; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D006026:Glycoside Hydrolases / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D007700:Kinetics; D008970:Molecular Weight; D013379:Substrate Specificity; D013696:Temperature; D013816:Thermodynamics; D014990:Xylans / Q000378:metabolism
chemical_list: D014990:Xylans; D006026:Glycoside Hydrolases; D043364:Endo-1,4-beta Xylanases