Polysaccharide charge fraction

Equations are derived from the Manning theory of polyelectrolyte solutions that permit the calculation of the charge fraction of ionic polysaccharides using experimental counterion and coion diffusion coefficients. Results are reported for the sodium salts of heparin, dextran sulfate, alginate and the calcium salt of heparin. 

Table I. A Comparison of the Experimental Charge Fraction with Those Predicted from the Manning Theory for Several Ionic Polysaccharides...

The polysaccharides present in the pectin-rich extract ChSS were fractionated, based on their charge density for further characterisation. The elution pattern of ChSS is shown in Figure 1, and it can be seen that the relative uronide content of the fractions increased with increasing salt concentration of the eluens. 

The development of electrophoretic techniques afforded possibilities for fractionations based on charge density differences. Duxbury (1989) has reviewed applications of different electrophoretic separation methods, including zone electrophoresis, moving boundary electrophoresis, isotachophoresis, and isoelectric focusing (IEF). Preparative column electrophoresis (Clapp, 1957) and continuous flow paper electrophoresis (Hayes, 1960 summarized by Hayes et al., 1985) methods have been used to separate components isolated from sapric histosol soils. These techniques allowed separation of polysaccharides from the colored components the electrophoretograms of the colored components were diffuse, showing a continuum of components of different charge densities. 

The difference between lEP and the net charge at a given pH of different proteins are the main factors enabling selective protein precipitation by anionic polysaccharides. This technique has been applied to the fractionation of milk and yeast proteins. At pH values below the lEP, anionic polysaccharides can also act as flocculants for... 

Vernhet, A., Pellerin, R, Prieur, C., Osmianski, J., Moutounet, M. (1996). Charge properties of some grape and wine polysaccharide and polyphenolic fractions. Am. J. Enol. Vitic., 47, 25-30. 

Electrophoresis is the term used to describe the movement of charged solute molecules in an electric field. Simple electrophoretic systems in which biological polymers were dissolved in buffer systems, placed on a variety of support media, and subjected to several hundred volts potential difference have yielded excellent results in the fractionation of proteins and polysaccharides. 

Electrophoretic separations of solutes are determined primarily by the mass-to-charge ratio of the solute. However, certain electrophoretic separations use gel or paper supports for the electrolyte, and adsorptive and molecular-size fractionations may be as significant as electrophoretic fractionation in these systems. Hall (1970) found that polyacrylamide gel electrophoresis of aquatic humic substances gave size fractionations corresponding to Sepha-dex gel fractionation however, individual fractions were poorly resolved in polyacrylamide gel electrophoresis. Clapp (1957) and Mortensen and Schwendinger (1963) used electrophoresis with electrolyte supporting curtains to separate colorless polysaccharides from humic substances in soil-water extracts. 

Some polysaccharides carry negative charges, by virtue of their uronic acid components and/or modification of OH groups as sulfate esters or cyclic acetals of pyruvic acid (CH3COCOOH) these can often be precipitated by cationic surfactants such as cetyltrimethylammonium bromide. They can also be fractionated on weak anion exchangers. For neutral polysaccharides, elaborate precipitation protocols involving initial removal of proteins and nucleic acids have to be used - a useful precipitant of the polysaccharide is 50% ethanol. 

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