Characterization of the lipid A component of genuine smooth‐form lipopolysaccharide

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Abstract
The smooth‐form lipopolysaccharide of Salmonella abortus equi had earlier been separated into three distinct fractions, a long‐chain fraction with an O chain containing 20–50 repeating units, a short‐chain fraction consisting of an R lipopolysaccharide and another with 1–6 repeating units, and an R fraction identical to the lipopolysaccharide synthesized by Ra, b‐mutant bacteria [Galanos et al. (1988) J. Chromatogr. 440, 397–404]. In this paper, the corresponding lipid A from each fraction was prepared by a newly elaborated procedure based on hydrolysis of the fractions in calcium acetate buffer (pH 3.5) followed by separation of the resulting free lipid A from the polysaccharide on a Sephadex G‐100 column. Chemical analysis revealed that lipid A of the R fraction contained the expected spectrum and amounts of fatty acids and it proved to be structurally identical to lipid A of previously studied Salmonella R mutants. In contrast, the lipid A of the long‐chain fraction contained only about 60% fatty acids compared to that of the R fraction. The lipid A of the short‐chain fraction also expressed a reduced substitution pattern of acyl residues.