Purification and properties of extracellular dextranase from a Bacillus sp.

摘要

Bacterial strains in the genus Bacillus were isolated from natural soil samples and screened for production of extracellular dextranases (E.C.3.2.1.11). One strain, determined by 16sRNA analysis as Paenibacillus illinoisensis exhibiting stable dextranase activity, was chosen for further analysis, and the dextranase from it was purified 733-fold using salt and PEG precipitations, two-phase extraction and DEAE-Sepharose chromatography with a total yield of 19%. The purified enzyme had three isoforms, with molecular masses of 76, 89 and 110 kDa and isoelectric points of 4.95, 4.2 and 4.0, respectively. The mixture of the three dextranase isoforms has a broad pH optimum around pH 6.8 and a temperature optimum at 50 ℃. The N-terminal sequence (Ala-Ser-Thr-Gly-Lys) was identical between the isoforms. No sequence homology with the known dextranases in the protein databanks was found.