PURIFICATION AND CHARACTERIZATION OF 2 THERMOSTABLE ENDO-1,4-BETA-D-XYLANASES FROM THERMOTOGA-THERMARUM

Two thermoactive endoxylanases (1,4-beta-D-xylan xylanohydrolase; EC 3 .2.1.8) were purified from the xylanolytic enzyme system of the thermo philic anaerobic bacterium Thermotoga thermarum. The dimeric enzyme en doxylanase I (M(r) values of 105 000 and 150 000) shows maximal activi ty at 80 degrees C and pH 6.0. Endoxylanase 2, which is composed of on e subunit (M(r) of 35 000), is more thermoactive and possesses maximal activity between 90 and 100 degrees C and at pH 7.0. Both enzymes are inactive towards CM-cellulose but, unlike endoxylanase I, endoxylanas e 2 is active towards galactomannan. The K-m and V-max values determin ed for endoxylanase I with 4-O-methyl-D-glucuronoxylan are 0.36 mg/ml and 1.18 units/mg of protein respectively. Endoxylanase 2, on the othe r hand, has a K-m value of 0.24 mg/ml and a V-max of 19.5 units/mg of protein.