Fluoride inhibition of enolase activity in vivo and its relationship to the inhibition of glucose-6-P formation in Streptococcus salivarius

Abstract

The intracellular concentrations of glucose-6-P, 2-P-glycerate, P-enolpyruvate, and pyruvate were determined in cells of Streptococcus salivarius metabolizing glucose in the presence and absence of NaF in an attempt to elucidate the mechanism of action of this inhibitor. The addition of 2.4 mm NaF to metabolizing whole cells resulted in a cessation of glucose uptake and an immediate decline in the cellular glucose-6-P content. A comparison of the 2-P-glycerate and P-enolpyruvate levels in treated and untreated cells indicated that fluoride had also inhibited intracellular enolase (EC 4.2.1.11) activity. These two apparently separate fluoride effects could not be separated regardless of the pH of the incubation medium (pH 7.2, 8.0, and 5.8), or the concentration of NaF added to the cells (final concentration, 2.4, 0.36, and 0.12 mm). The addition of 2.4 mm NaF to cells metabolizing intracellular glycogen at pH 7.2 also resulted in the inhibition of enolase activity; however, in this case, inhibition of cellular glucose-6-P synthesis was not observed. These results indicated that fluoride was directly involved in the inhibition of glucose-6-P formation from exogenous glucose. The possible relationship between the two fluoride-sensitive sites was made clear by the demonstration that the P-enolpyruvate-phosphotransferase system was involved in the transport of glucose into cells of S. salivarius. The evidence strongly suggests that the fluoride inhibition of enolase results in the inhibition of glucose transport by reducing the amount of P-enolpyruvate available for phosphorylation.