Significance of a p-nitrophenylphosphatase for Streptococcus mutans

Abstract

The hydrolysis of p-nitrophenyl phosphate (added to the incubation medium), catalyzed by a Mg-dependent and highly specific p-nitrophenylphosphatase, stimulated the uptake of K⁺ ions by the cells of Streptococcus mutans. The stimulation was detectable only in the presence of glucose and it was highest at 0.1–0.2 mM concentrations of p-nitrophenyl phosphate. The degree of stimulation was also dependent on the extracellular concentrations of K⁺ ions. The rate of the hydrolysis of p-nitrophenyl phosphate, catalyzed by both the cells and the purified enzyme, was not affected by K⁺ ions and dicyclohexylcarbodiimide. The other cleavage product of the hydrolysis of p-nitrophenyl phosphate (p-nitrophenol) inhibited the uptake of K⁺ and phosphate ions, but it did not affect the activity of ATP:ase of the cells.