Macromolecular Structure of Lipopolysaccharides from Gram‐Negative Bacteria

Abstract

The cell wall lipopolysaccharide constituent of Shigella flexneri, Salmonella typhimurium and Salmonella minnesota appears in the electron microscope as long slender filaments having a molecular weight of several millions. Such lipopolysaccharides are constituted of subunits held together by low‐energy bonds of chelating and hydrophobic nature due to the lipid part of the molecule. Physicochemical studies gave molecular weights in the range of 18000 to 25000 for the subunits of S strains depending upon the bacterial species, and 10000 in the case of the Salmonella minnesota R mutants. The subunits seem to be long ellipsoids of revolution made up of a lipid part and two polysaccharide side chains. Studies of the dissociation and the reassociation of the lipopolysaccharide subunits showed the existence of a cylindrical intermediate “unit structure” having a molecular weight of about 5·10 5 . The arrangement of the subunits in that unit structure seems to be of a micellar type, the lipids being located in the central part of this structure. This latter model is compatible with a skew arrangement of unit structures into the larger polymer molecules.