ISOLATION AND CHARACTERIZATION OF A THERMOSTABLE DEXTRANASE

A thermostable dextranase has been isolated from an anaerobic thermoph ilic bacterium, Rt364, collected from a New Zealand thermal spring. Th e enzyme was purified by ammonium sulfate precipitation and successive ion exchange, hydrophobic interaction, and size exclusion chromatogra phies. The enzyme exhibited an apparent molecular weight of similar to 140 kDa, a temperature optimum of 80 degrees C, and a pH optimum of s imilar to 5.5. The enzyme was extremely stable. No activity was lost o ver 12 h at 75 degrees C. It is more thermostable than the dextranase from Chaetomium gracile, the most thermostable dextranase previously c haracterized; however, the Rt364 dextranase has a much lower specific activity, 10 U mg(-1), compared to 2,750 U mg(-1) for the fungal enzym e at their respective temperature optima. The enzyme from Rt364 hydrol yzes dextran, starch, amylose, and amylopectin with approximately the same catalytic efficiencies but does not hydrolyze pullulan. It has th erefore been designated an amylodextranase which is analogous to the r ecently characterized amylopullulanase. (C) 1997 by Elsevier Science I nc.