Fig. 1. Structures of E. coli and R. leguminosarum lipid A and of Kdo₂-[4′-³²P]lipid IV_A.

A, the 1-, 3-, and 4′-positions of each lipid A structure are indicated. Evidence for the presence of an acyloxyacyl residue and partially deacylated species has recently been presented by Que et al. (25, 26). B, the same seven enzymes catalyze the formation of Kdo₂-lipid IV_A in both organisms (29). A phosphoenzyme intermediate could explain all of the reactions catalyzed by the 4′-phosphatase/phosphotransferase of R. leguminosarum.