Lipopolysaccharides (LPS) are found in the cell wall of Gram-negative bacteria i.e.
those that do retain the gram-stain. Given the general formula for enterobacterial
lipopolysaccharides with an O-polysaccharide, a core and a lipid A, treatment with
dilute acetic acid cleaves the ketosidic linkages of the Kdo residues.
The specific details of the O-polysaccharide, the core and the lipid A varies substantially. If the O-polysaccharide is present, then the bacteria are called smooth, if it is absent they are then called rough. The repeating units, shown in brackets above, are distributed over a range say 10-40 can be shown by sodium-dodecyl sulphate polyacrylamide gel electrophoreses (SDS-PAGE) where a ladder pattern is seen. A phosphate group at position 4 of the branch point Kdo often results in an elimination reaction and "anhydro-Kdo" is formed i.e. a Kdo molecule that formally has lost water. The result of the delipidation is thus a free O-polysaccharide linked to a modified core (with only one Kdo) and free lipid A. The delipidation is also sometimes performed in detergent when there are real solubility problems or when heterogeneous product mixtures are obtained.