The Reassociation of Lipopolysaccharide, Phospholipid, and Transferase Enzymes of the Bacterial Cell Envelope

The components of the uridine diphosphate galactose:lipopolysaccharide α-3-galactosyltransferase system from Salmonella typhimurium were studied. Binary complexes (lipopolysaccharide-phospholipid) and ternary complexes (enzyme-lipopolysaccharide-phospholipid), previously postulated as intermediates in lipopolysaccharide biosynthesis, were reconstituted from the purified components. The complexes were isolated and characterized by sucrose gradient centrifugation. The association of phospholipid with lipopolysaccharide did not require a fixed molar ratio of the two components, and the binary complex appeared to be a multimolecular complex of the two components. The reconstituted complexes showed restoration of activity in the UDP-galactose:lipopolysaccharide α-3-galactosyltransferase system. The apparent role of phosphatidylethanolamine was to promote binding of the enzyme to its lipopolysaccharide substrate.