Nature and location of amide‐bound ( R )‐3‐acyloxyacyl groups in lipid A of lipopolysaccharides from various gram‐negative bacteria

It has previously been demonstrated [ Eur. J. Biochem. 124 , 191–198 (1982) and 137 , 15–22 (1983)] that the lipid A component of Salmonella and Proteus lipopolysaccharides contains amide‐linked ( R )‐3‐acyloxyacyl residues. In the present study lipid A of other gram‐negative bacteria was analysed for the presence of amide‐bound 3‐acyloxyacyl residues. It was found that such residues are constituents of all lipid A tested ( Agrobacterium tumefaciens, Chromobacterium violaceum, Pseudomonas aeruginosa, Xanthomonas sinensis, Bacteriodes fragilis, Vibrio cholerae, Fusobacterium nucleatum, Rhodospirillum tenue, Acinetobacter calcoaceticus , and Escherichia coli ). Amide‐linked ( R )‐3‐acyloxyacyl groups, therefore, represent common and ubiquitous structural elements of bacterial lipid A. The composition of 3‐acyloxyacyl groups differed considerably among different bacteria. As amide‐bound ( R )‐3‐hydroxy fatty acids straight chain and isobranched acyl groups with 10–17 carbon atoms were identified. The most frequently encountered fatty acids, substituting the 3‐hydroxyl group of 3‐hydroxy fatty acids, were nonhydroxylated straight chain and isobranched acyl residues with 10–17 carbon atoms as well as ( S )‐2‐hydroxy fatty acids with 12 carbon atoms. In some cases, using laser desorption mass spectrometry, the distribution of 3‐acyloxyacyl residues over the two available glucosamine amino groups of the lipid A backbone was investigated.