Purification,properties, and mode of action of hemicellulase II produced by Ceratocystis paradoxa |
| |
Authors: | Robert FH Dekker Geoffrey N Richards |
| |
Institution: | Department of Chemistry and Biochemistry, James Cook University of North Queensland, Townsville Australia |
| |
Abstract: | An extra-cellular endo-hemicellulase (HC-II) from a culture isolate of the fungal plant pathogen Ceratocystis paradoxa (CP2) was purified 147-fold by ammonium sulphate precipitation, DEAE-Sephadex chromatography, iso-electric focusing at pH 3–10, and gel-permeation chromatography. The resulting enzyme preparation, which contained traces of invertase, gave a single protein-band on disc electrophoresis at pH 8.4, and was active towards sucrose, hemicellulose, and carboxymethylcellulose (CMC). HC-II randomly degraded hemicelluloses from several different sources, to xylose and to arabinose-xylose and xylose oligosaccharides of d.p. 3–6 and 2–5, respectively, and also produced a degraded hemicellulose which precipitated from the digest solution. The precipitated hemicellulose contained less arabinose and uronic acid than the original hemicellulose. When redissolved by alkali-treatment, it was susceptible to further degradation by hemicellulases HC-I and HC-II. CMC was degraded by HC-II, mainly to D-glucose and cellobiose, with trace amounts of unidentified higher oligosaccharides, while cellobiose remained unattacked. Xylotriose (Xyl3) was the lowest homologue of the xylose oligosaccharides attacked by HC-II at a significant rate, yielding xylobiose Xyl2; β-D-Xylp-(1→4)-D-Xyl] and xylose. AraXyl3AraXyl5 were mainly hydrolysed to AraXyl2, xylose, and Xyl2 or Xyl3. HC-II had a temperature optimum of 80°, and was stable for 1 h at temperatures up to 70°. The pH optimum was 5.1, and HC-II was stable between pH 5–10. The Km was 0.267 mg of hemicellulose B/ml. The effects of mercury(II) ions and high concentrations of xylose on the activity of HC-II were also investigated. |
| |
Keywords: | To whom communications should be addressed |
本文献已被 ScienceDirect 等数据库收录! |
|