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. 1993 Jun;59(6):1725–1730. doi: 10.1128/aem.59.6.1725-1730.1993

Purification and characterization of a thermostable xylanase from Bacillus stearothermophilus T-6.

A Khasin 1, I Alchanati 1, Y Shoham 1
PMCID: PMC182151  PMID: 8328796

Abstract

Bacillus stearothermophilus T-6 produces an extracellular xylanase that was shown to optimally bleach pulp at pH 9 and 65 degrees C. The enzyme was purified and concentrated in a single adsorption step onto a cation exchanger and is made of a single polypeptide with an apparent M(r) of 43,000 (determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Xylanase T-6 is an endoxylanase that completely degrades xylan to xylose and xylobiose. The pIs of the purified protein were 9 and 7 under native and denaturing conditions, respectively. The optimum activity was at pH 6.5; however, 60% of the activity was still retained at pH 10. At 65 degrees C and pH 7, the enzyme was stable for more than 10 h; at 65 degrees C and pH 9, the half-life of the enzyme was approximately 6 h. Kinetic experiments at 55 degrees C gave Vmax and Km values of 288 U/mg and 1.63 mg/ml, respectively. The enzyme had no apparent requirement for cofactors, and its activity was strongly inhibited by Zn2+, Cd2+, and Hg2+. Xylan completely protected the protein from inactivation by N-bromosuccinimide. The N-terminal sequence of the first 45 amino acids of the enzyme showed high homology with the N-terminal region of xylanase A from the alkalophilic Bacillus sp. strain C-125.

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Selected References

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