Isolation, Purification and Properties of an Intermediate in 3‐Deoxy‐ d ‐manno‐octulosonic Acid—Lipid A Biosynthesis

Incomplete lipid A has been purified from a mutant of Salmonella typhimurium which is temperature‐sensitive both in synthesis of 3‐deoxy‐ d ‐manno‐octulosonic acid 8‐phosphate (dOclA‐8‐ P ) and in growth. Pulse‐chase experiments have shown that the incomplete lipid A molecule is the intermediate in the biosynthesis of the dOclA‐lipid A portion of lipopolysaccharides. The purification procedure included DEAE‐cellulose chromatography and electrodialysis. A highly water‐soluble precursor material was obtained, consisting of glucosamine, phosphate and 3‐hydroxymyristic acid in a molar ratio of 1:1.2:2.1. Labeling experiments as well as chemical degradation procedures revealed the precursor molecule to be composed of a diphosphorylated glucosamine‐disaccharide carrying two amide‐linked and two ester‐linked 3‐hydroxymyristic acids. In contrast to the complete dOclA‐lipid A part, the intermediate lacks 3‐deoxy‐ d ‐manno‐octulosonic acid as well as nonhydroxy‐lated fatty acids. On the basis of these findings a pathway for the final steps in dOclA‐lipid A biosynthesis is proposed.