FIGURE 2.

Charge deconvoluted ESI FT-ICR mass spectra in negative ion mode of LPS molecules isolated from E. coli strains KPM56 (A) and KPM125 (B). M1, lipid IV_A (1404.85 u); M2, lipid IV_A modified with a P-EtN group (1527.86 u); M3, Kdo-lipid IV_A (1624.91 u); M4, Kdo-lipid IV_A substituted with a P-EtN group (1747.92 u). Peaks presumably representing molecules with variations in acyl chain length (Δm = 14.02 u) are labeled with an asterisk. The molecule corresponding to triacylated lipid A (1178.66 u) is probably an artifact produced during LPS isolation, since it is not consistent with a known pathway intermediate.