AN EXTREMELY THERMOSTABLE XYLANASE FROM THE THERMOPHILIC EUBACTERIUM THERMOTOGA

Endo-1,4-beta-xylanase (EC 3.2.1.8) was isolated from the culture supernatant of Thermotoga sp. strain FjSS3-B.1, an extremely thermophilic anaerobic eubacterium which grows optimally at 80-degrees-C. Activity was purified 165-fold by anion-exchange and hydroxyapatite chromatography. The enzyme has an M(r) of 31 000 as determined by SDS/PAGE and 35 000 by analytical gel filtration. The optima for activity and stability for purified xylanase were between pH 5.0 and 5.5. At pH 5.5, which is the optimum pH for thermostability, t1/2 (95-degrees-C) is 90 min. The thermostability was improved by immobilization of the xylanase on to porous glass beads; t1/2 (105-degrees-C) is 10 min. Several additives, such as sorbitol and xylan, were also found to increase the thermostability. At 130-degrees-C, the half-life of immobilized xylanase in the presence of 90% sorbitol was 1.3 min. At 130-degrees-C in molten sorbitol half of the enzyme denatured rapidly, but the remainder appeared to have a half-life of about 60 min.