Purification and characterization of a thermophilic alkaline xylanase from thermoalkaliphilic Bacillus sp strain TAR-1

Thermoalkaliphilic Bacillus sp. strain TAR-1 isolated from soil produced an extracellular xylanase. The enzyme (xylanase R) was purified to homogeneity by ammonium sulfate fractionation and anion-exchange chromatography. The molecular mass of xylanase R was 40 kDa and the isoelectric point was 4.1. The enzyme was most active over the range of pH 5.0 to 10.0 at 50 degrees C. The optimum temperatures for activity were 75 degrees C at pH 7.0 and 70 degrees C at pH 9.0. Xylanase R was stable up to 65 degrees C at pH 9.0 for 30 min in the presence of xylan. Mercury(II) ion at 1 mM concentration abolished all the xylanase activity. The predominant products of xylan-hydrolysate were xylobiose, xylotriose, and higher oligosaccharides, indicating that xylanase R was an endo-acting enzyme. Xylanase R had a K-m of 0.82 mg/ml and a V-max of 280 mu mol min(-1) mg(-1) for xylan at 50 degrees C and pH 9.0.