Involved in the biosynthesis of the polysaccharide xanthan. 30-40% of the terminal mannose residues of xanthan have a 4,6-O-(1-carboxyethan-1,1-diyl) ketal group. It also acts on the 6-O-acetyl derivative of the inner mannose unit.
the mutant strain is unable to synthesize the pyruvylated intermediate in vitro. Enzyme activity is not essential for polysaccharide production since inactivation of gumL does not affect polymerization. gumL mutants are not affected in growth and produce normal nonpyruvylated polymer levels