Electrodialysis of lipopolysaccharides and their conversion to uniform salt forms

Abstract

Ions of low molecular weight like metal cations and basic amines are present in lipopolysaccharides regardless of the isolation procedure employed. They are present in salt form with the acidic groups of the molecule and, partly, bound by chelation. Electrodialysis which removed a large proportion of these basic materials led to acidic lipopolysaccharides often with reduced solubility. Electrodialyzed lopopolysaccharides could be rendered soluble by neutralizing with alkali or with a basic amine. Depending on the base employed for neutralization preparations were obtained which showed in water distinct differences in solubility, viscosity and opalescence. These differences were related to differences in the sedimentation coefficients of the various salt forms. Neutralization with triethylamine led in all cases to highly soluble preparations with low sedimentation coefficients, while, on the other hand, neutralization with Mg(OH)2 led in most cases to insoluble preparations. The acidic lipopolysaccharides obtained by electrodialysis deteriorate on storing in a freeze-dried form. On heating in distilled water autohydrolysis occurs and free lipid A is liberated. The lipid A which is so far known as a water-insoluble material showed increased solubility when prepared from electrodialyzed lipopolysaccharides.