Pyruvic acid acetal residues are transferred from phosphoenolpyruvate to the pentasaccharide-P-P-lipid

Xanthan gum is a complex polysaccharide produced by Xanthomonas campestris , composed of pentasaccharide repeating units containing mannose, glucose and glucuronic acid (in the ratio 2:2:1) and pyruvic acid acetal and O-acetyl residues in differing proportions. Previous work has shown that the pentasaccharide is first assembled on a pyrophosphate lipid and then polymerized to xanthan gum. It is now shown, using EDTA-treated cells and different combinations of the adequate ( super(14)C)labeled donors, that phosphoenol pyruvate provides the acetal residues and that the transfer occurs on the terminal mannose of the pentasaccharide-P-P-lipid, as judged by the solubility properties and DEAE-cellulose column chromatography of the compounds formed as well as by the behaviour of the substances liberated by mild acid and alkaline treatments and Smith degradation. The subsequent polymerization process leads to pyruvylated xanthan gum.