Gram-negative Endotoxin: A Biologically Active Lipid

The outer membrane of gram-negative bacteria such as Escherichia coli (Nikaido and Vaara 1987) consists of proteins, glycerophospholipids, and lipopolysaccharide (LPS) (Fig. 1). The lipid A component of LPS is unusual in that it is a fatty acylated derivative of glucosamine (see Figs. 2 and 3) instead of glycerol Raetz 1986,1987). The disposition of lipids in the outer membrane of E. coli is highly asymmetrical (Nikaido and Vaara 1987). The lipid A component of LPS makes up the outer monolayer of the outer membrane, whereas glycerophospholipids make up the inner monolayer.