Purification and characterization of two thermostable endo-1,4-β-D-xylanases from Thermotoga thermarum

Two thermoactive endoxylanases (1,4-β-D-xylan xylanohydrolase; EC 3.2.1.8) were purified from the xylanolytic enzyme system of the thermophilic anaerobic bacterium Thermotoga thermarum. The dimeric enzyme endoxylanase 1 (M(r) values of 105,000 and 150,000) shows maximal activity at 80°C and pH 6.0. Endoxylanase 2, which is composed of one subunit (M(r) of 35,000), is more thermoactive and possesses maximal activity between 90 and 100°C and at pH 7.0. Both enzymes are inactive towards CM-cellulose but, unlike endoxylanase 1, endoxylanase 2 is active towards galactomannan. The K(m) and V(max) values determined for endoxylanase 1 with 4-O-methyl-D-glucuronoxylan are 0.36 mg/ml and 1.18 units/mg of protein respectively. Endoxylanase 2, on the other hand, has a K(m) value of 0.24 mg/ml and a V(max) of 19.5 units/mg of protein.