ENZYMATIC SYNTHESIS OF DEXTRAN

Dextran, a glucose polymer composed predominantly of ol-1,6-glucopyranosidic linkages, is produced from sucrose by Leuconostoc mesenteroides and related organisms and from dextrins by other bacteria (see the review by Hehre (1)). Conversion of sucrose to dextran is catalyzed by an enzyme, dextransucrase, elaborated by the organisms. Dextransucrase preparations as culture filtrates (2, 3) or as dry purified concentrates are prepared readily and some of the properties of the enzyme have been described (2-5). A study of the course of enzymatic dextran synthesis indicated that dextran having an average molecular weight of several millions is produced from the beginning of reaction. In recent experiments it has been found that the presence of certain sugars, notably maltose and isomaltose, as auxiliary sugars in dextran-synthesizing reaction mixtures alters the normal course of reaction so that the usual opalescent, viscous type of solution, indicative of extensive high polymer production, is not obtained. Such reaction mixtures contain instead oligosaccharides as major products. It appeared that the auxiliary sugars acted as glucosyl acceptors, alternate with the normal acceptor, and also initiated chain formati0n.l A study of acceptor specificity in dextran synthesis was therefore undertaken with the object of elucidating the polymerization mechanism. It was hoped that clues leading to the direct enzymatic synthesis of “clinical” dextran with an average molecular weight in the range of 50,000 to 100,000 would be found. The results are described here.