Role of the cell membrane in pH-dependent fluoride inhibition of glucose uptake by Streptococcus mutans

The effect of pH on the fluoride sensitivity of glucose uptake by whole cells and glucose transport by permeabilized cells of Streptococcus mutans was compared. Whole cells exhibited a marked pH-dependent sensitivity to fluoride over the pH range 7.0 to 5.0. As the pH was decreased, fluoride sensitivity increased. In contrast, no significant effect of pH on the fluoride sensitivity of glucose transport (e.g., phosphorylation) by permeabilized cells energized with 2-phosphoglycerate was noted. The relative effect of pH on the fluoride sensitivity of whole cell glucose uptake and fermentation was similar. These data are consistent with the notion that the cell membrane is impermeable to the fluoride anion and that intracellular accumulation of fluoride depends on translocation of hydrogen fluoride across the membrane.