Dextran-degrading Enzymes from Molds1

Enzymes capable of degrading dextran, the polymer of glucose produced from sucrose by the action of Leuconostoc mesenteroides and related organisms, are potentially valuable for fundamental research as well as for practical application. Although the a-i ,6-glucopyranosidic linkage is present to the extent of 95 per cent or more in some easily obtainable dextrans, the only other known occurrence of this linkage is the 5 to 10 per cent found in starch, glycogen, and similar polysaccharides. Thus, as has been pointed out previously by Jeanes et al. (1948), dextran provides a unique source of simpler carbohydrates containig the a-1 ,6-glucosidic linkage obtainable through enzymic degradation. Enzymes produced by organisms grown on dextran and capable of cleaving the 1,6 linkage may be useful in studies concerning starch structure. And lastly, as has been indicated already by Ingelman (1948) and by Whiteside-Carlson and Carlson (1952), 'ther types of dextranases offer a means for degrading dextran to molecular size range suitable for use as synthetic blood volume expanders. Although in this paper the term "dextranase" is used in the singular, we recognize the possibility of there being more than one enzyme that degrades dextran. Furthermore, a microorganism may produce more than one type of dextran-depolymerizing enzyme. There are reported here our observations on the occurrence, production, and activity of certain mold enzymes that degrade dextran from Leuconostoc mesenteroides, strain NRRL B-512, to diand higher oligosaccharides. This dextran is a linear type which contains approximately 95 per cent a-i, 6-glucosidic linkages (Jeanes and Wilham, 1950). In our search for dextran-hydrolyzing enzymes, begun in 1945, we have screened approximately 200 strains of bacteria, yeasts, and molds for their ability to produce extracellular dextranase. Like van Tieghem (1878), Colin and Belval (1940), and others, we were unable to find organisms producing large amounts of the enzyme among bacteria and yeasts. Ingeiman (1948) has reported a low order of dextranase activity from Cellvibrio fulva. Recently, Hehre and Sery (1952) have isolated dextran-splitting anaerobic bacteria from the h an intestine. Independently of Hultin and Nordstr6m (1948, 1949), we found that certain strains of Penicillia produced extracellular dextranase, but in small amounts. However, when we tested the species of Penicillia used by Hultin and