Biochemical Studies on Lipopolysaccharides of Salmonella R Mutants

In an in vitro system, containing 20,000 × g cell wall particles and 100,000 × g cell sap supernatant of various Salmonella rough mutants the rate of galactose transfer from UDP‐[ 14 C]‐galactose to the core lipopolysaccharide was studied and the following results obtained:1 Cell wall partieles from the S. minnesota mutants mR5, mR7, and mR8 are poor acceptors for galactose. The lipopolysaccharides of these mutants contain heptose and phosphate in a molar ratio of 2:2, whereas in normal lipopolysaccharide of Salmonella the ratio is 2:3. 2 20,000 × g cell wall fractions from mutants which produce lipopolysaccharide of normal phosphate content, such as those from S. minnesota mRz or S. typhimurium tmM are good acceptors for galactose. 3 Phosphate‐poor cell wall particles can be treated with ATP and enzyme extracts of mutants containing lipopolysaccharide of normal phosphate content to yield proper acceptors for galactose. 4 A radioactive disaccharide which chromatographically behaves like melibiose, and which after treatment with α‐galactosidase yields [ 14 C]galactose can be isolated from partial hydrolysates of cell wall particles which have previously been incubated with UDP‐[ 14 C]galactose and enzyme extract from tmM. This result is the same whether phosphate is already present in the cell wall fraction or is introduced enzymatically by the addition of ATP to the incubation mixture.It is concluded that mR5 and mR8 are defective in a lipopolysaccharide phosphorylating enzyme and that lack of phosphate groups in the lipopolysaccharide results in an incomplete core because unphosphorylated lipopolysaccharide acts only as a poor acceptor in the galactose transfer reaction.