Purification and characterization of intracellular dextranase of Bacteroides oralis Ig4a

Multiple forms of dextranase were detected in both intra- and extracellular fractions of Bacteroides oralis Ig4a. The molecular weights of these enzymes varied from 52,000 to 260,000 by sodium dodecyl sulfate-polyacrylamide-blue dextran gel electrophoresis. The intracellular dextranases were fractionated by chromatography and gel filtration steps, and the dextranases IV and V were obtained. The former was only partially pure. The molecular weights of the dextranases IV and V were estimated to be 120,000 and 105,000, respectively, by SDS-PAGE. The dextranase V was further characterized and it was revealed that the pH- and temperature optima were 5.0, and 55 degrees C, respectively. The Km value was 6.7 x 10(-2) mM for dextran T-70. The enzyme did not exhibit any metal ion requirements, but was inhibited by CoCl2 and HgCl2; lysine and alanine contents were especially high; it hydrolyzed the alpha-1,6-glucan by an exo-type mechanism, and was inactive toward glucans containing alpha-1,3-, alpha-1,4-, and beta-1,4-linkages.