Fig. 6.

Negative-ion MALDI MS/MS spectrum of precursor ion at m/z 1673.7, a representative ion peak of the cluster ascribed to mono-phosphorylated penta-acylated lipid A species detected for Z. profunda SM-A87 LipA_me. The assignment of main fragments is shown in the spectrum alongside with the proposed structure that is sketched in the inset. The nature of branched acyl chains (iso) in the depicted lipid A structure is given for description purposes only. Peaks derived by the loss of C₁₅H₃₀O (226 mass units), as a consequence of the rearrangement occurring on N-linked 3-OH acyl chains having the hydroxyl group free, have been also indicated