Location and identification of substituents with free amino group in lipopolysaccharides of gram-negative bacteria with the use of chromophore labelling

Interaction of ten different lipopolysaccharides (LPS) with 2,4-dinitrofluorobenzene yielded quantitatively yellow dinitrophenyl derivatives (DNP-LPS) to show the presence of substituents with free amino group. The DNP-LPS samples were degraded with 1% acetic acid, and after removal of lipid A precipitates the supernatants were separated on a Sephadex G-25 column to give coloured polysaccharide, oligosaccharide and monomeric fractions monitored at lambda DNP = 365 nm. The coloured materials, including DNP-derivative of lipid A, were dephosphorylated with hydrofluoric acid followed by identification of the released DNP-amines by thin layer chromatography (TLC) on silica gel. Subsequently, the dephosphorylated materials were hydrolysed with hydrochloric acid followed by TLC analysis. The approach allowed to detect, locate and identify the substituents with free amino group within the LPS molecules. Moreover, two types of core structures within LPS preparation from one strain were discovered for five microorganisms.