Enolases from fluoride-sensitive and fluoride-resistant streptococci

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Abstract
The enolases from a highly fluoride-sensitive strain of Streptococcus salivarius and its fluoride-resistant mutant, and those from strains of S. sanguis and S. mutans with intermediate and low sensitivities to fluoride, have been shown to be inhibited by fluoride. Comparisons of the purified, strain-specific enzymes showed a high degree of similarity for all preparations. The Km for the substrate 2-phosphoglycerate were 1.3 .times. 10-4 to 2.4 .times. 10-4 M, pH optima were 7.3-7.7, and Mg2+ optima were 2 mEq/l for all. Inhibition by fluoride required the presence of inorganic phosphate and was competitive in nature, and the calculated modified inhibition indices were found to be in the range from 3.3 .times. 10-14 to 5.8 .times. 10-14 M4. Percent inhibitions were determined under standardized conditions (0.16 mM NaF, 2 mM MgSO4, 0.5 mM Pi and 0.5 mM 2-phosphoglycerate) and ranged from 53.3 to 65.9% for all of the purified enzymes. The differences do not appear to be meaningful metabolically. Inhibition was reduced to about 14% at pH 6.0. From the similarities in the behavior of the strain-specific enzymes it is concluded that the differences in the glycolytic sensitivities of the different strains of streptococci to fluoride are not the consequence of any kinetic differences between the respective enolases.