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An extremely thermostable xylanase from the thermophilic eubacterium Thermotoga.

ABSTRACT: 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 Mr 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.

SUBMITTER: Simpson HD

PROVIDER: S-EPMC1151249 | biostudies-other | 1991 Jul

REPOSITORIES: biostudies-other

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Project description:Phosphate acetyltransferase (PTA) and acetate kinase (AK) of the hyperthermophilic eubacterium Thermotoga maritima have been purified 1,500- and 250-fold, respectively, to apparent homogeneity. PTA had an apparent molecular mass of 170 kDa and was composed of one subunit with a molecular mass of 34 kDa, suggesting a homotetramer (alpha4) structure. The N-terminal amino acid sequence showed significant identity to that of phosphate butyryltransferases from Clostridium acetobutylicum rather than to those of known phosphate acetyltransferases. The kinetic constants of the reversible enzyme reaction (acetyl-CoA + Pi -->/<-- acetyl phosphate + CoA) were determined at the pH optimum of pH 6.5. The apparent Km values for acetyl-CoA, Pi, acetyl phosphate, and coenzyme A (CoA) were 23, 110, 24, and 30 microM, respectively; the apparent Vmax values (at 55 degrees C) were 260 U/mg (acetyl phosphate formation) and 570 U/mg (acetyl-CoA formation). In addition to acetyl-CoA (100%), the enzyme accepted propionyl-CoA (60%) and butyryl-CoA (30%). The enzyme had a temperature optimum at 90 degrees C and was not inactivated by heat upon incubation at 80 degrees C for more than 2 h. AK had an apparent molecular mass of 90 kDa and consisted of one 44-kDa subunit, indicating a homodimer (alpha2) structure. The N-terminal amino acid sequence showed significant similarity to those of all known acetate kinases from eubacteria as well that of the archaeon Methanosarcina thermophila. The kinetic constants of the reversible enzyme reaction (acetyl phosphate + ADP -->/<-- acetate + ATP) were determined at the pH optimum of pH 7.0. The apparent Km values for acetyl phosphate, ADP, acetate, and ATP were 0.44, 3, 40, and 0.7 mM, respectively; the apparent Vmax values (at 50 degrees C) were 2,600 U/mg (acetate formation) and 1,800 U/mg (acetyl phosphate formation). AK phosphorylated propionate (54%) in addition to acetate (100%) and used GTP (100%), ITP (163%), UTP (56%), and CTP (21%) as phosphoryl donors in addition to ATP (100%). Divalent cations were required for activity, with Mn2+ and Mg2+ being most effective. The enzyme had a temperature optimum at 90 degrees C and was stabilized against heat inactivation by salts. In the presence of (NH4)2SO4 (1 M), which was most effective, the enzyme did not lose activity upon incubation at 100 degrees C for 3 h. The temperature optimum at 90 degrees C and the high thermostability of both PTA and AK are in accordance with their physiological function under hyperthermophilic conditions.

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An extremely thermostable xylanase from the thermophilic eubacterium Thermotoga.

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