Biological Activities of Chemically Modified Endotoxins.

The cell wall glycolipid (somatic antigen) of the Re mutant of Salmonella minnesota is comparable in its endotoxic activity to the complete wild type lipopolysaccharide. The glycolipid is composed mainly of lipid A and 2-keto-3-deoxyoctonate (KDO); smaller amounts of ethanolamine and 4-aminoarabinose, and traces of amino acids are also present. The serological specificity is determined by KDO residues. In order to determine if non-lipid A constituents contribute to endotoxicity, amino groups and KDO units in the glycolipid were chemically modified by the introduction of substituents. When free amino groups were dinitrophenylated or succinylated the serological specificity was unaffected. By contrast, the original serological specificity was completely lost when the free hydroxyl groups of the KDO region were substituted with succinyl residues or the carboxyl groups converted to the methyl esters. In biological tests, however, the modified preparations exhibited full endotoxic activity. It is concluded that the polar groups, which determine the serological specificity of the KDO region of the glycolipid, do not play a specific role in endotoxicity. [ABSTRACT FROM AUTHOR]