Hudson, R.C., Schofield, L.R., Coolbear, T., Daniel, R.M. & Morgan, H.W. (1991). Purification and properties of an aryl beta-xylosidase from a cellulolytic extreme thermophile expressed in Escherichia coli. Biochemical Journal, 273(3), 645-650.
Permanent Research Commons link: http://hdl.handle.net/10289/4497
An aryl beta-xylosidase was purified to homogeneity from an Escherichia coli strain containing a recombinant plasmid carrying a beta-xylosidase (EC 18.104.22.168) gene from the extremely thermophilic anaerobic bacterium isolate Tp8T22.214.171.124 ('Caldocellum saccharolyticum'). It has a pI of 4.3 and shows optimal activity at pH 5.7. The enzyme is highly specific, acting on o- and p-nitrophenyl beta-D-xylopyranosides and minimally on p-nitrophenyl alpha-L-arabinopyranoside. It does not act on xylobiose. The Km for p-nitrophenyl beta-D-xylopyranoside at the optimum pH for activity is 10 mM, and at pH 7.0 is 6.7 mM. Xylose is a competitive inhibitor with Ki 40 mM. Thermal inactivation follows first-order kinetics at 65 and 70 degrees C with t1/2 values of 4.85 h and 40 min respectively. The t1/2 at 70 degrees C is increased 3-fold and 4-fold by the addition of 0.5 mg of BSA/ml and 2 mM-dithiothreitol respectively.