Molds of 514 strains were screened for their ability to produce extracellular dextranase. Seven strains out of them producing dextranse were isolated, and among the seven strains one showed distinguished enzyme activity of dextranase which was identified to be Aspergillus ustus. The most suitable cultural conditions of the enzyme were investigated.
Maximal dextranase activity was showed when grown aerobically at 28℃ in a medium containing 1% dextran, 2% yeast extract together with trace amount of inorganic salts at pH 8.0.
Dextranase from A. ustus (EC 3, 2, 1, 11) was purified about 70-folds by means of acetone precipitation and of a repeated chromatography on a column of DEAE-cellulose, Bio Gel P-150 and Sephadex G-200.
The optimal pH of the purified dextranase was 6.5 and this enzyme was maximally activated at 40℃. The thermal stability was stable at temperature below 50℃. The enzyme was markedly inactivated by Hg, Cu, KCN, Co and to extend Ba, Fe, cysteine, EDTA and Ascorbic acid.
The main product of hydrolysis of dextran incubated with dextranase was glucose, isomaltotriose and oligosaccharide (4∼20 dextrose polymer chain). When dextran was incubated with dextranase plus pullzyme and α-amylase, it was hydrolyzed into glucose, isomaltotriose, isomaltose and oligosaccharide (4∼15 dextrose polymer chain). Teeth powder (polysaccharides) was hydrolyzed into glucose, isomaltotriose and oligosaccharides. In the teeth powder hydrolysis, coaction of pullzyme and α-amylase was similar to the dextranase hydrolysis.
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