Neutral, Microbial Polysaccharides of Commercial Importance

Strain NRRL B-512(F) produces large proportions of the extracellular enzyme dextransucrase,339 which is responsible for the synthesis of linear sequences ofa-D-(l — 6)-linked D-glucosyl residues. The enzyme transfers the D-glucosyl group from a sucrose molecule to an enlarging dextran chain and liberates the D-fructose portion. As dextransucrase is an extracellular enzyme, production of dextran by cell-free, culture filtrates can result in enhanced yield and quality, and ease of purification of the product. By suitable adjustment of the conditions, products in a chosen molecular-weight range can be obtained. Formation of branches is not yet well understood, but the enzymes responsible will certainly be found. 

Methods for the depolymerization of dextran to uniform fractions of lower molecular weight have led to the use of two dextran fractions that are suitable for parenteral administration.13,30 In the United States, a dextran fraction of MW 70,000 is used as a blood-volume expander. Clinical dextran is used to restore blood volume in the treatment of patients who have either lost considerable amounts of blood or are in shock. A dextran fraction of MW 40,000 is used to improve the flow in capillaries, to prevent or treat vascular occlusion, and to perfuse organs artifically. B-512(F) dextran is completely metabolized141 in man when fractions are administered parentally. Various dextran fractions have been used to prepare numerous derivatives,29 such as the sulfates, and 0-(2-diethylaminoethyl) (DEAE)-dextran, and complexes with various metals. Dextran sulfates have anticoagulant,340 antilipemic,340 and anti-ulcer341 activity. A soluble, iron-dextran complex342 of MW 5000 is used to alleviate iron-deficiency anemia, and a calcium complex332 alleviates hypocalcemia of cattle. 

Crosslinked dextran gels (for example, Sephadex ) have been used extensively for the purification and fractionation of various biological substances, including the recovery of proteins from liquid wastes and effluent streams.343 -347 

Dextran is used in gel precipitation for purifying, separating,347,348 and concentrating metals for use as nuclear-reactor fuels,349,350 catalysts,350-352 ceramic coatings,349 refractories, ferro-electric materials,351,352 and pigments.353 

Many uses of dextran in petroleum production have been proposed. It has been tested successfully for use in drilling muds,354,355 and in viscous water-flooding.356,357 The patent literature332 suggests that the native, high-molecular-weight dextran is now used in various proprietary, X-ray and photographic emulsions. 

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