Purification and characterization of a levanase from Streptomyces sp. 366L

Abstract

A levanase-producing microorganism was isolated from soil and identified as genus Streptomyces. The enzyme was purified to homogeneity by several procedures including ammonium sulfate fractionation, DEAE-Toyopearl 650M ion exchange chromatography, phenyl-Toyopearl 650M hydrophobic chromatography, Sephadex G-200 gel filtration, and hydroxyapatite adsorption chromatography. The molecular mass of the enzyme was estimated to be 78 000 by SDS-polyacrylamide disc gel electrophoresis and 80 000 by gel filtration. The isoelectric point of the enzyme was pH 4.1 and activity was optimal at pH 7.0 and 40°C. In 30 min reactions, the enzyme was stable at the pH range of 6.0–10.0 at 20°C and remained stable up to 45°C at pH 7.0. The enzyme hydrolyzed levan to produce levanheptaose predominantly and showed an absolute substrate specificity for levan. When incubated with levans from Serratia sp. and Zymomonas mobilis, the enzyme hydrolyzed about 81 and 61%, respectively.