PURIFICATION, CHARACTERIZATION AND REGULATION OF THE SYNTHESIS OF AN ASPERGILLUS-NIDULANS ACIDIC XYLANASE

An acidic xylanase from a culture filtrate of Aspergillus nidulans gro wn on oat-spelt xylan was purified to apparent homogeneity. The purifi ed enzyme showed a single band on sodium dodecyl sulphate-polyacrylami de gel electrophoresis with a molecular mass of 34,000 Da and had an i soelectric point of approximately 3.4. The enzyme was a non-debranchin g endoxylanase highly specific for xylans. The xylanase showed an opti mal activity at pH 6.0 and 56 degrees C and had a Michaelis constant K -m of 0.97 mg oat-spelt xylan (soluble fraction) mi and a maximed reac tion velocity (Vmax) of 1,091 mu mol min(-1) (mg(-1)protein)(-1). Usin g polyclonal antibodies raised against the purified enzyme, the regula tion of its synthesis has been studied. The xylanase production is rep ressed by glucose and induced by oat-spelt xylan, arabinoxylan, 4-O-me thylglucurono-xylan, birchwood xylan and xylose.