Biosynthesis of Salmonella Lipopolysaccharide

Several transfer reactions involved in the biosynthesis of the core part of Salmonella lipopolysaccharide have been studied in a cell free system. This system contained three components: (1) enzymes which were solubilised by repeated washings of EDTA‐lysozyme spheroplasts; (2) acceptor which consisted of either a heated cell wall fraction sedimenting at 20 000 x g, or heated, partially lysed, EDTA‐lysozyme treated cells; and (3) radioactively labelled precursors ([32P]ATP, UDP‐[14C]Glc, UDP‐[14C]Gal). The following results were obtained with this transfer system: (1) only the γ‐phosphate group of ATP is transferred to the heptose moiety of the core; (2) polyphosphate which is synthesised enzymatically in a a side‐reaction by the system is not involved in the heptose phosphorylation; (3) there is a definite sequence of addition of the core substituents glucose, phosphate, and galactose to the incomplete core stub. This sequence is as follows: (Hep)2‐(KDO, ethanolamine, phosphate, lipid A) → Glc‐(Hep)2‐(KDO, ethanolamine, phosphate, lipid A) → Glc‐(Hep)2P‐(KDO, ethanolamine, phosphate, lipid A) → (Gal)2‐Glc‐(Hep)2P‐(KDO, ethanolamine, phosphate, lipid A).