Biosynthesis of bacterial lipopolysaccharide. VII. Enzymatic formation of the first intermediate in biosynthesis of the O-antigen of Salmonella typhimurium.

The initial step in biosynthesis of the O-antigen of Salmonella typhimurium is the formation of a lipid-linked derivative of galactose l-phosphate, according to the reaction UDP-galactose + P-lipid ti galactose-1 -PP-lipid + UMP. The enzyme activity has been detected in the cell envelope fraction of Citrobocter strain 139 (04, 5, 12) as well as in wild type S. typhimurium strain LT-2, but is most readily demonstrated in cell envelope fractions obtained from a mutant strain of S. fyphimurium lacking UDP-galactose 4epimerase following growth in the presence of galactose. The enzyme catalyzes transfer of the entire galactose lphosphate moiety of UDP-galactose to the lipid acceptor with concomitant formation of stoichiometric amounts of UMP. The reaction is readily reversible, with an apparent equilibrium constant of approximately 0.5.