Purification and some properties of Thermotoga neapolitana thermostable xylanase B expressed in E. coli cells.

A xylanase was purified from the recombinant strain E. coli TG1 carrying the pTT32 vector with a fragment of the Thermotoga neapolitana chromosomal DNA. The enzyme was purified 419-fold with 36% yield after heating at 70 degrees C and pH 4.5 and subsequent ion-exchange chromatography. By polyacrylamide gel electrophoresis in the presence of SDS, the molecular weight of the apparently homogeneous protein is 39 kD. By isoelectric focusing, the protein is of a single form with pI = 5.9. The optimal pH for hydrolysis is 5.5, and the optimal temperature is 90 degrees C. The xylanase is stable to heating at 70 degrees C for 4 h. The enzyme is inactivated by 50% at 80, 90, and 100 degrees C after 227, 162, and 30 min, respectively. Enzyme activity was tested using xylans and glucans as substrates. By thin-layer chromatography of the xylan hydrolysis products, the enzyme was classified as an endoxylanase.