dextrans

High-molecular weight polysaccharides synthesied by some microorganisms. Consist of D-glucose linked by a -1,6 bonds (and a few a -1,3 and a -1,4 bonds). Dextran 75 (average molecular weight 75 kD) has a colloid osmotic pressure similar to blood plasma, so dextran 75 solutions are used clinically as plasma expanders. They will also cause charge-shielding, and at the right concentrations induce flocculation of red cells, a trick that is used in preparing leucocyte-rich plasma for white cell purification in the laboratory. Cross-linked dextran is the basis for Sephadex. Commercially derived from strains of Leuconostoc mesenteroides.