Highly thermostable xylanase purified fromRhizomucor mieheiNRL 3169

Abstract

A thermostable xylanase was purified and characterized from the thermophilic fungus Rhizomucor miehei\ud (Cooney & Emerson) Schipper. The enzyme was purified to homogeneity by ammonium sulfate precipitation,\ud sephadex G-100 gel filtration and diethylaminoethyl cellulose anion exchange chromatography with\ud a 29.1-fold. The enzyme was highly active within a range of pH from 5.0 to 6.5. The optimum temperature\ud of the purified enzyme was 75 °C. The enzyme showed high thermal stability at 70 °C and 75 °C and\ud the half-life of the xylanase at 90 °C was 30 min. Km and Vmax values at 50 °C of the purified enzyme\ud were 0.055 mg/ml and 113.5 μmol min−1 mg−1, respectively. The enzyme was activated by Ca2+, Cu2+, K+\ud and Na+. On the other hand, Ag2+, Hg2+, Ba2+, and Zn2+ inhibited the enzyme. The molecular weight of\ud the xylanase was estimated to be 27 kDa by sodium dodecyl sulfate–polyacrylamide gel electrophoresis.\ud The present study is among the first works to examine and describe a secreted highly thermostable\ud endoxylanase from the Rhizomucor miehei fungus. This enzyme displays a number of biochemical properties\ud that make it a potentially strong candidate for industrial and commercial application in pulp bleaching