An endoxylanase (1,4-beta -D-xylan xylanohydrolase, EC 126.96.36.199) was produced by Rhizopus oryzae fermentation. Different xylan-containing agricultural byproducts such as wheat straw, wheat stems, cotton bagasse, hazelnut shells, corn cobs and oat sawdust were used as the carbon source, white soybean bagasse was used as both the nitrogen and carbon source in the enzyme production medium. Partial steam hydrolysis of the agricultural byproducts increased the enzyme yield of the microorganism, The highest xylanase activity, 260 IU/ml fermentation medium, was obtained by using a medium containing 3% hydrolyzed com cobs, 1% hydrolyzed soybean bagasse, 1% ammonium sulfate and 0.5% sodium chloride at 35 degreesC, pH 5, 350 rpm and under aerobic conditions in a 2-1 fermenter. A maximal cellulose activity of 0.06 IU/ml was observed. The enzyme was partially purified from the culture medium by ammonium sulfate precipitation and cation exchange filtration. A 55-fold purification was achieved, with the purified xylanase having a specific activity of about 50 IU/mg protein. The molecular weight of the enzyme is about 22 kDa by SDS-PAGE. The optimal pH and temperature values of the enzyme were about 4.5 and 55 degreesC, respectively. The enzyme obeys Michaelis-Menten kinetics with Km and V. values being 18.5 mg xylan/ml and 90 IU/mg protein, respectively. (C) 2001 Elsevier Science Inc. All rights reserved.