[Purification, characterization of an extracellular dextranase from an isolated Penicillium sp]

To obtain new fungi producing dextranase,we screened and identified a strain F1001 showing high dextranase activities. We provided a new strain with dextranase activity for producing clinical dextran.

Morphological and ITS rDNA sequences homology analysis were performed to identify the strain F1001. The enzyme was purified to electrophoretic homogeneity by the steps of ammonium sulfate precipitation and Sepharose 6B column chromatography. We studied the catalytic properties and the mechanism of the dextranase, and activities of dextranase were measured with dextran 70 kDa as the substrate.

The isolated strain F1001 was identifed as Penicillium aculeatum precisely by ITS rDNA sequences homology analysis. Its molecular mass was estimated to be about 66 kDa by SDS-PAGE. The optimal reaction temperature was 35 degrees C, and the optimum pH was 5.0, it was stable in the condition of pH 4.0 - 7.0 and under the temperature of 50 degrees C. The optimum substrate concentration was 3% (w/v). The final dextranase hydrolysis product was isomaltose, which proved that the enzyme was endodextranase and only had activity with dextran joined mainly by continual alpha, 1-6 glucosidic linkages. The K(m) for dextranase was calculated to be 3.55 x 10(-5) mol/L, and the V(max) was 4.29 x 10(-2) mol (Glu)/min x L. The enzyme activity was enhanced by Zn2+ and Cu2+, and the low concentration of Cu2+ could improve the dextranase activity to 134.7%. However, the enzyme was strongly inhibited by Mn2+.

We isolated a new strain F1001 producing high dextranase activity and the enzyme was stable. These results may provide an important basis for industrial applications.