On the production of dextran by free and immobilized dextransucrase

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Abstract
Dextransucrase from Leuconostoc mesenteroides was produced in a semicontinuous culture with slow addition of a concentrated sucrose solution. The resulting high activity of the fermentation broth allowed a one‐step purification method, by gel permeation chromatography (GPC) in 96.4% yield. This procedure resulted in 140‐fold purification, with specific activity of 122 U/mg. The enzyme was immobilized onto an amino‐Spherosil support activated with glutaraldehyde. Preparations with dextransucrase activities as high as 40.5 U/g of support were obtained, when low specific area supports were used and maltose was added during the enzyme coupling. Diffusional limitations were found during enzyme reaction, as shown by a kinetic study. As a consequence of immobilization, the average molecular weight of dextrans seems to increase. Immobilized dextransucrase looks promising for low‐molecular‐weight dextran production. Clinical dextran was synthesized when the polysaccharides produced in the presence of maltose were used as acceptor of a second synthesis reaction. The molecular weight distribution of the resulting production was less disperse than when clinical dextran was produced by acid hydrolysis of high‐molecular‐weight dextran.