Effect of novel compound, 1-methyl-1-piperidino methane sulfonate (MPMS), on the osmoprotectant activity of glycine betaine, choline and L-proline in Escherichia coli.

A novel compound, 1-methyl-1-piperidino methane sulfonate (MPMS), was found to block the osmoprotectant activity of choline and L-proline, but not glycine betaine in Escherichia coli. MPMS was more active against salt-sensitive than salt-resistant strains, but had no effect on the salt tolerance of a mutant which was unable to transport choline, glycine betaine and proline. Growth of E. coli in NaCl was inhibited by MPMS and restored by glycine betaine, but not by choline or L-proline. Uptake of radiolabeled glycine betaine, choline or L-proline by cells grown at high osmolarity was not inhibited when MPMS and the radioactive substrates were added simultaneously. Preincubation for 5 min with MPMS reduced the uptake of choline and L-proline, but not glycine betaine. Similar incubation with MPMS had no effect on the uptake of radiolabeled glucose or succinate. The toxicity of MPMS was much lower than that of the L-proline analogues L-azetidine-2-carboxylic acid and 3,4-dehydro-DL-proline. The exact mechanism by which MPMS exerts its effect is not entirely clear. MPMS or a metabolite may interfere with the activity of several independent permeases involved in the uptake of osmoprotective compounds, or the conversion of choline to glycine betaine, or effect the expression of some of the osmoregulatory genes.