Thermoalkalophilic Arthrobacter sp. produced extracellular xylanase, when wheat bran, rice husk, rice bran and bagassae were used as carbon source under solid-state fermentation (SSF). The xylanase enzyme was isolated by ammonium sulfate (80%) fractionation, and purified to homogeneity using size exclusion and ion exchange chromatography. The molecular mass of xylanase was similar to 20 kDa. Enzyme retained 100% activity at pH 7 and 8 for 24 h. It was interesting to note that at higher pH such as 9, 10 and 11 the enzyme activity increased over the period of incubation. The optimum temperature for the enzyme activity was 100 degrees C at pH 9.0. At 80 degrees C and pH 9, half-life of enzyme was 30 min. Half-life of enzyme at 70 and 60 degrees C was 18 and 24 h, respectively. While at 50 degrees C the-enzyme retained 79% of activity even after 48 h. For xylan, the enzyme gave a K-m value of 0.9 mg/ml, and V-max value of 3571 mu mol/min/mg when the reaction was carried out at 100 degrees C and pH 9. In the presence of metal ions such as Co2+, Zn2+, Fe2+, Cu2+, Mg2+ and Ca2+ and metal chelator EDTA the activity of the enzyme increased. Whereas strong inhibition of the enzyme activity was observed in the presence of Hg2+. These are some novel characteristics that make this enzyme potentially very effective for industrial applications. (c) 2005 Elsevier Inc. All rights reserved.