Location of fatty acids in lipid A obtained from lipopolysaccharide of Rhodopseudomons sphaeroides ATCC 17023

Monophosphoryl lipid A (MLA) obtained from the lipopolysaccharide of Rhodopseudomonas sphaeroides ATCC 17023 was initially purified by silicic acid column chromatography to yield a single major pentaacyl MLA fraction. This fraction was methylated and further purified by reverse-phase high performance liquid chromtography to yield three prominent peak fractions. Laser desorption mass spectrometry of these three fractions allowed us to complete the important structural analysis of lipid A from this source. Three structurally distinct forms of dimethyl MLAwere identified where M(r) = 1447, 1449, and 1451 atomic mass units. These forms differed only by the presence or absence of unsaturation and keto group in the fatty acids. We established that the acyloxyacyl group (either Δ⁷-tetradecenoyloxytetradecanoate or tetradecanoyloxytetradecanoate) and the 3-ketotetradecanoate or hydroxytertadecanoate occupied the 2'- and 2-positions of the glucosamine disaccharide, respectively. Analysis of several minor fractions suggests that there is considerable structural heterogeneity in the MLA. With this new knowledge, the study of the structure-to-function relationship of the reported lack of toxicity of lipopolysaccharide from R. sphaeroides can be completed.