FIGURE 1.
Lipid A analysis of E. coli and S. flexneri 2a LPS preparations used in this study. Monophosphoryl lipid A prepared from the LPS of E. coli K235 and S. flexneri 2a was analyzed by mass spectrometry (A and B, respectively) as described in Materials and Methods. Analysis of the two LPS preparations by MS revealed that, while the lipid A from E. coli LPS was predominantly hexaacylated (A), the lipid A from S. flexneri 2a LPS was predominantly tetraacylated (where the myristoxymyristate was missing from the 3′ position of the glucosamine dissacharide), pentaacylated (the hydroxymyristate was missing from the 3-position) and hexaacylated forms were also present (B). This analysis was carried out on two separate preparations of S. flexneri 2a with similar results.